mm,hugetlb: use folio fields in second tail page

[linux.git] / mm / shmem.c

/*
 * Resizable virtual memory filesystem for Linux.
 *
 * Copyright (C) 2000 Linus Torvalds.
 *               2000 Transmeta Corp.
 *               2000-2001 Christoph Rohland
 *               2000-2001 SAP AG
 *               2002 Red Hat Inc.
 * Copyright (C) 2002-2011 Hugh Dickins.
 * Copyright (C) 2011 Google Inc.
 * Copyright (C) 2002-2005 VERITAS Software Corporation.
 * Copyright (C) 2004 Andi Kleen, SuSE Labs
 *
 * Extended attribute support for tmpfs:
 * Copyright (c) 2004, Luke Kenneth Casson Leighton <[email protected]>
 * Copyright (c) 2004 Red Hat, Inc., James Morris <[email protected]>
 *
 * tiny-shmem:
 * Copyright (c) 2004, 2008 Matt Mackall <[email protected]>
 *
 * This file is released under the GPL.
 */

#include <linux/fs.h>
#include <linux/init.h>
#include <linux/vfs.h>
#include <linux/mount.h>
#include <linux/ramfs.h>
#include <linux/pagemap.h>
#include <linux/file.h>
#include <linux/fileattr.h>
#include <linux/mm.h>
#include <linux/random.h>
#include <linux/sched/signal.h>
#include <linux/export.h>
#include <linux/swap.h>
#include <linux/uio.h>
#include <linux/hugetlb.h>
#include <linux/fs_parser.h>
#include <linux/swapfile.h>
#include <linux/iversion.h>
#include "swap.h"

static struct vfsmount *shm_mnt;

#ifdef CONFIG_SHMEM
/*
 * This virtual memory filesystem is heavily based on the ramfs. It
 * extends ramfs by the ability to use swap and honor resource limits
 * which makes it a completely usable filesystem.
 */

#include <linux/xattr.h>
#include <linux/exportfs.h>
#include <linux/posix_acl.h>
#include <linux/posix_acl_xattr.h>
#include <linux/mman.h>
#include <linux/string.h>
#include <linux/slab.h>
#include <linux/backing-dev.h>
#include <linux/shmem_fs.h>
#include <linux/writeback.h>
#include <linux/pagevec.h>
#include <linux/percpu_counter.h>
#include <linux/falloc.h>
#include <linux/splice.h>
#include <linux/security.h>
#include <linux/swapops.h>
#include <linux/mempolicy.h>
#include <linux/namei.h>
#include <linux/ctype.h>
#include <linux/migrate.h>
#include <linux/highmem.h>
#include <linux/seq_file.h>
#include <linux/magic.h>
#include <linux/syscalls.h>
#include <linux/fcntl.h>
#include <uapi/linux/memfd.h>
#include <linux/userfaultfd_k.h>
#include <linux/rmap.h>
#include <linux/uuid.h>

#include <linux/uaccess.h>

#include "internal.h"

#define BLOCKS_PER_PAGE  (PAGE_SIZE/512)
#define VM_ACCT(size)    (PAGE_ALIGN(size) >> PAGE_SHIFT)

/* Pretend that each entry is of this size in directory's i_size */
#define BOGO_DIRENT_SIZE 20

/* Symlink up to this size is kmalloc'ed instead of using a swappable page */
#define SHORT_SYMLINK_LEN 128

/*
 * shmem_fallocate communicates with shmem_fault or shmem_writepage via
 * inode->i_private (with i_rwsem making sure that it has only one user at
 * a time): we would prefer not to enlarge the shmem inode just for that.
 */
struct shmem_falloc {
        wait_queue_head_t *waitq; /* faults into hole wait for punch to end */
        pgoff_t start;          /* start of range currently being fallocated */
        pgoff_t next;           /* the next page offset to be fallocated */
        pgoff_t nr_falloced;    /* how many new pages have been fallocated */
        pgoff_t nr_unswapped;   /* how often writepage refused to swap out */
};

struct shmem_options {
        unsigned long long blocks;
        unsigned long long inodes;
        struct mempolicy *mpol;
        kuid_t uid;
        kgid_t gid;
        umode_t mode;
        bool full_inums;
        int huge;
        int seen;
#define SHMEM_SEEN_BLOCKS 1
#define SHMEM_SEEN_INODES 2
#define SHMEM_SEEN_HUGE 4
#define SHMEM_SEEN_INUMS 8
};

#ifdef CONFIG_TMPFS
static unsigned long shmem_default_max_blocks(void)
{
        return totalram_pages() / 2;
}

static unsigned long shmem_default_max_inodes(void)
{
        unsigned long nr_pages = totalram_pages();

        return min(nr_pages - totalhigh_pages(), nr_pages / 2);
}
#endif

static int shmem_swapin_folio(struct inode *inode, pgoff_t index,
                             struct folio **foliop, enum sgp_type sgp,
                             gfp_t gfp, struct vm_area_struct *vma,
                             vm_fault_t *fault_type);

static inline struct shmem_sb_info *SHMEM_SB(struct super_block *sb)
{
        return sb->s_fs_info;
}

/*
 * shmem_file_setup pre-accounts the whole fixed size of a VM object,
 * for shared memory and for shared anonymous (/dev/zero) mappings
 * (unless MAP_NORESERVE and sysctl_overcommit_memory <= 1),
 * consistent with the pre-accounting of private mappings ...
 */
static inline int shmem_acct_size(unsigned long flags, loff_t size)
{
        return (flags & VM_NORESERVE) ?
                0 : security_vm_enough_memory_mm(current->mm, VM_ACCT(size));
}

static inline void shmem_unacct_size(unsigned long flags, loff_t size)
{
        if (!(flags & VM_NORESERVE))
                vm_unacct_memory(VM_ACCT(size));
}

static inline int shmem_reacct_size(unsigned long flags,
                loff_t oldsize, loff_t newsize)
{
        if (!(flags & VM_NORESERVE)) {
                if (VM_ACCT(newsize) > VM_ACCT(oldsize))
                        return security_vm_enough_memory_mm(current->mm,
                                        VM_ACCT(newsize) - VM_ACCT(oldsize));
                else if (VM_ACCT(newsize) < VM_ACCT(oldsize))
                        vm_unacct_memory(VM_ACCT(oldsize) - VM_ACCT(newsize));
        }
        return 0;
}

/*
 * ... whereas tmpfs objects are accounted incrementally as
 * pages are allocated, in order to allow large sparse files.
 * shmem_get_folio reports shmem_acct_block failure as -ENOSPC not -ENOMEM,
 * so that a failure on a sparse tmpfs mapping will give SIGBUS not OOM.
 */
static inline int shmem_acct_block(unsigned long flags, long pages)
{
        if (!(flags & VM_NORESERVE))
                return 0;

        return security_vm_enough_memory_mm(current->mm,
                        pages * VM_ACCT(PAGE_SIZE));
}

static inline void shmem_unacct_blocks(unsigned long flags, long pages)
{
        if (flags & VM_NORESERVE)
                vm_unacct_memory(pages * VM_ACCT(PAGE_SIZE));
}

static inline bool shmem_inode_acct_block(struct inode *inode, long pages)
{
        struct shmem_inode_info *info = SHMEM_I(inode);
        struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);

        if (shmem_acct_block(info->flags, pages))
                return false;

        if (sbinfo->max_blocks) {
                if (percpu_counter_compare(&sbinfo->used_blocks,
                                           sbinfo->max_blocks - pages) > 0)
                        goto unacct;
                percpu_counter_add(&sbinfo->used_blocks, pages);
        }

        return true;

unacct:
        shmem_unacct_blocks(info->flags, pages);
        return false;
}

static inline void shmem_inode_unacct_blocks(struct inode *inode, long pages)
{
        struct shmem_inode_info *info = SHMEM_I(inode);
        struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);

        if (sbinfo->max_blocks)
                percpu_counter_sub(&sbinfo->used_blocks, pages);
        shmem_unacct_blocks(info->flags, pages);
}

static const struct super_operations shmem_ops;
const struct address_space_operations shmem_aops;
static const struct file_operations shmem_file_operations;
static const struct inode_operations shmem_inode_operations;
static const struct inode_operations shmem_dir_inode_operations;
static const struct inode_operations shmem_special_inode_operations;
static const struct vm_operations_struct shmem_vm_ops;
static struct file_system_type shmem_fs_type;

bool vma_is_shmem(struct vm_area_struct *vma)
{
        return vma->vm_ops == &shmem_vm_ops;
}

static LIST_HEAD(shmem_swaplist);
static DEFINE_MUTEX(shmem_swaplist_mutex);

/*
 * shmem_reserve_inode() performs bookkeeping to reserve a shmem inode, and
 * produces a novel ino for the newly allocated inode.
 *
 * It may also be called when making a hard link to permit the space needed by
 * each dentry. However, in that case, no new inode number is needed since that
 * internally draws from another pool of inode numbers (currently global
 * get_next_ino()). This case is indicated by passing NULL as inop.
 */
#define SHMEM_INO_BATCH 1024
static int shmem_reserve_inode(struct super_block *sb, ino_t *inop)
{
        struct shmem_sb_info *sbinfo = SHMEM_SB(sb);
        ino_t ino;

        if (!(sb->s_flags & SB_KERNMOUNT)) {
                raw_spin_lock(&sbinfo->stat_lock);
                if (sbinfo->max_inodes) {
                        if (!sbinfo->free_inodes) {
                                raw_spin_unlock(&sbinfo->stat_lock);
                                return -ENOSPC;
                        }
                        sbinfo->free_inodes--;
                }
                if (inop) {
                        ino = sbinfo->next_ino++;
                        if (unlikely(is_zero_ino(ino)))
                                ino = sbinfo->next_ino++;
                        if (unlikely(!sbinfo->full_inums &&
                                     ino > UINT_MAX)) {
                                /*
                                 * Emulate get_next_ino uint wraparound for
                                 * compatibility
                                 */
                                if (IS_ENABLED(CONFIG_64BIT))
                                        pr_warn("%s: inode number overflow on device %d, consider using inode64 mount option\n",
                                                __func__, MINOR(sb->s_dev));
                                sbinfo->next_ino = 1;
                                ino = sbinfo->next_ino++;
                        }
                        *inop = ino;
                }
                raw_spin_unlock(&sbinfo->stat_lock);
        } else if (inop) {
                /*
                 * __shmem_file_setup, one of our callers, is lock-free: it
                 * doesn't hold stat_lock in shmem_reserve_inode since
                 * max_inodes is always 0, and is called from potentially
                 * unknown contexts. As such, use a per-cpu batched allocator
                 * which doesn't require the per-sb stat_lock unless we are at
                 * the batch boundary.
                 *
                 * We don't need to worry about inode{32,64} since SB_KERNMOUNT
                 * shmem mounts are not exposed to userspace, so we don't need
                 * to worry about things like glibc compatibility.
                 */
                ino_t *next_ino;

                next_ino = per_cpu_ptr(sbinfo->ino_batch, get_cpu());
                ino = *next_ino;
                if (unlikely(ino % SHMEM_INO_BATCH == 0)) {
                        raw_spin_lock(&sbinfo->stat_lock);
                        ino = sbinfo->next_ino;
                        sbinfo->next_ino += SHMEM_INO_BATCH;
                        raw_spin_unlock(&sbinfo->stat_lock);
                        if (unlikely(is_zero_ino(ino)))
                                ino++;
                }
                *inop = ino;
                *next_ino = ++ino;
                put_cpu();
        }

        return 0;
}

static void shmem_free_inode(struct super_block *sb)
{
        struct shmem_sb_info *sbinfo = SHMEM_SB(sb);
        if (sbinfo->max_inodes) {
                raw_spin_lock(&sbinfo->stat_lock);
                sbinfo->free_inodes++;
                raw_spin_unlock(&sbinfo->stat_lock);
        }
}

/**
 * shmem_recalc_inode - recalculate the block usage of an inode
 * @inode: inode to recalc
 *
 * We have to calculate the free blocks since the mm can drop
 * undirtied hole pages behind our back.
 *
 * But normally   info->alloced == inode->i_mapping->nrpages + info->swapped
 * So mm freed is info->alloced - (inode->i_mapping->nrpages + info->swapped)
 *
 * It has to be called with the spinlock held.
 */
static void shmem_recalc_inode(struct inode *inode)
{
        struct shmem_inode_info *info = SHMEM_I(inode);
        long freed;

        freed = info->alloced - info->swapped - inode->i_mapping->nrpages;
        if (freed > 0) {
                info->alloced -= freed;
                inode->i_blocks -= freed * BLOCKS_PER_PAGE;
                shmem_inode_unacct_blocks(inode, freed);
        }
}

bool shmem_charge(struct inode *inode, long pages)
{
        struct shmem_inode_info *info = SHMEM_I(inode);
        unsigned long flags;

        if (!shmem_inode_acct_block(inode, pages))
                return false;

        /* nrpages adjustment first, then shmem_recalc_inode() when balanced */
        inode->i_mapping->nrpages += pages;

        spin_lock_irqsave(&info->lock, flags);
        info->alloced += pages;
        inode->i_blocks += pages * BLOCKS_PER_PAGE;
        shmem_recalc_inode(inode);
        spin_unlock_irqrestore(&info->lock, flags);

        return true;
}

void shmem_uncharge(struct inode *inode, long pages)
{
        struct shmem_inode_info *info = SHMEM_I(inode);
        unsigned long flags;

        /* nrpages adjustment done by __filemap_remove_folio() or caller */

        spin_lock_irqsave(&info->lock, flags);
        info->alloced -= pages;
        inode->i_blocks -= pages * BLOCKS_PER_PAGE;
        shmem_recalc_inode(inode);
        spin_unlock_irqrestore(&info->lock, flags);

        shmem_inode_unacct_blocks(inode, pages);
}

/*
 * Replace item expected in xarray by a new item, while holding xa_lock.
 */
static int shmem_replace_entry(struct address_space *mapping,
                        pgoff_t index, void *expected, void *replacement)
{
        XA_STATE(xas, &mapping->i_pages, index);
        void *item;

        VM_BUG_ON(!expected);
        VM_BUG_ON(!replacement);
        item = xas_load(&xas);
        if (item != expected)
                return -ENOENT;
        xas_store(&xas, replacement);
        return 0;
}

/*
 * Sometimes, before we decide whether to proceed or to fail, we must check
 * that an entry was not already brought back from swap by a racing thread.
 *
 * Checking page is not enough: by the time a SwapCache page is locked, it
 * might be reused, and again be SwapCache, using the same swap as before.
 */
static bool shmem_confirm_swap(struct address_space *mapping,
                               pgoff_t index, swp_entry_t swap)
{
        return xa_load(&mapping->i_pages, index) == swp_to_radix_entry(swap);
}

/*
 * Definitions for "huge tmpfs": tmpfs mounted with the huge= option
 *
 * SHMEM_HUGE_NEVER:
 *      disables huge pages for the mount;
 * SHMEM_HUGE_ALWAYS:
 *      enables huge pages for the mount;
 * SHMEM_HUGE_WITHIN_SIZE:
 *      only allocate huge pages if the page will be fully within i_size,
 *      also respect fadvise()/madvise() hints;
 * SHMEM_HUGE_ADVISE:
 *      only allocate huge pages if requested with fadvise()/madvise();
 */

#define SHMEM_HUGE_NEVER        0
#define SHMEM_HUGE_ALWAYS       1
#define SHMEM_HUGE_WITHIN_SIZE  2
#define SHMEM_HUGE_ADVISE       3

/*
 * Special values.
 * Only can be set via /sys/kernel/mm/transparent_hugepage/shmem_enabled:
 *
 * SHMEM_HUGE_DENY:
 *      disables huge on shm_mnt and all mounts, for emergency use;
 * SHMEM_HUGE_FORCE:
 *      enables huge on shm_mnt and all mounts, w/o needing option, for testing;
 *
 */
#define SHMEM_HUGE_DENY         (-1)
#define SHMEM_HUGE_FORCE        (-2)

#ifdef CONFIG_TRANSPARENT_HUGEPAGE
/* ifdef here to avoid bloating shmem.o when not necessary */

static int shmem_huge __read_mostly = SHMEM_HUGE_NEVER;

bool shmem_is_huge(struct vm_area_struct *vma, struct inode *inode,
                   pgoff_t index, bool shmem_huge_force)
{
        loff_t i_size;

        if (!S_ISREG(inode->i_mode))
                return false;
        if (vma && ((vma->vm_flags & VM_NOHUGEPAGE) ||
            test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags)))
                return false;
        if (shmem_huge_force)
                return true;
        if (shmem_huge == SHMEM_HUGE_FORCE)
                return true;
        if (shmem_huge == SHMEM_HUGE_DENY)
                return false;

        switch (SHMEM_SB(inode->i_sb)->huge) {
        case SHMEM_HUGE_ALWAYS:
                return true;
        case SHMEM_HUGE_WITHIN_SIZE:
                index = round_up(index + 1, HPAGE_PMD_NR);
                i_size = round_up(i_size_read(inode), PAGE_SIZE);
                if (i_size >> PAGE_SHIFT >= index)
                        return true;
                fallthrough;
        case SHMEM_HUGE_ADVISE:
                if (vma && (vma->vm_flags & VM_HUGEPAGE))
                        return true;
                fallthrough;
        default:
                return false;
        }
}

#if defined(CONFIG_SYSFS)
static int shmem_parse_huge(const char *str)
{
        if (!strcmp(str, "never"))
                return SHMEM_HUGE_NEVER;
        if (!strcmp(str, "always"))
                return SHMEM_HUGE_ALWAYS;
        if (!strcmp(str, "within_size"))
                return SHMEM_HUGE_WITHIN_SIZE;
        if (!strcmp(str, "advise"))
                return SHMEM_HUGE_ADVISE;
        if (!strcmp(str, "deny"))
                return SHMEM_HUGE_DENY;
        if (!strcmp(str, "force"))
                return SHMEM_HUGE_FORCE;
        return -EINVAL;
}
#endif

#if defined(CONFIG_SYSFS) || defined(CONFIG_TMPFS)
static const char *shmem_format_huge(int huge)
{
        switch (huge) {
        case SHMEM_HUGE_NEVER:
                return "never";
        case SHMEM_HUGE_ALWAYS:
                return "always";
        case SHMEM_HUGE_WITHIN_SIZE:
                return "within_size";
        case SHMEM_HUGE_ADVISE:
                return "advise";
        case SHMEM_HUGE_DENY:
                return "deny";
        case SHMEM_HUGE_FORCE:
                return "force";
        default:
                VM_BUG_ON(1);
                return "bad_val";
        }
}
#endif

static unsigned long shmem_unused_huge_shrink(struct shmem_sb_info *sbinfo,
                struct shrink_control *sc, unsigned long nr_to_split)
{
        LIST_HEAD(list), *pos, *next;
        LIST_HEAD(to_remove);
        struct inode *inode;
        struct shmem_inode_info *info;
        struct folio *folio;
        unsigned long batch = sc ? sc->nr_to_scan : 128;
        int split = 0;

        if (list_empty(&sbinfo->shrinklist))
                return SHRINK_STOP;

        spin_lock(&sbinfo->shrinklist_lock);
        list_for_each_safe(pos, next, &sbinfo->shrinklist) {
                info = list_entry(pos, struct shmem_inode_info, shrinklist);

                /* pin the inode */
                inode = igrab(&info->vfs_inode);

                /* inode is about to be evicted */
                if (!inode) {
                        list_del_init(&info->shrinklist);
                        goto next;
                }

                /* Check if there's anything to gain */
                if (round_up(inode->i_size, PAGE_SIZE) ==
                                round_up(inode->i_size, HPAGE_PMD_SIZE)) {
                        list_move(&info->shrinklist, &to_remove);
                        goto next;
                }

                list_move(&info->shrinklist, &list);
next:
                sbinfo->shrinklist_len--;
                if (!--batch)
                        break;
        }
        spin_unlock(&sbinfo->shrinklist_lock);

        list_for_each_safe(pos, next, &to_remove) {
                info = list_entry(pos, struct shmem_inode_info, shrinklist);
                inode = &info->vfs_inode;
                list_del_init(&info->shrinklist);
                iput(inode);
        }

        list_for_each_safe(pos, next, &list) {
                int ret;
                pgoff_t index;

                info = list_entry(pos, struct shmem_inode_info, shrinklist);
                inode = &info->vfs_inode;

                if (nr_to_split && split >= nr_to_split)
                        goto move_back;

                index = (inode->i_size & HPAGE_PMD_MASK) >> PAGE_SHIFT;
                folio = filemap_get_folio(inode->i_mapping, index);
                if (!folio)
                        goto drop;

                /* No huge page at the end of the file: nothing to split */
                if (!folio_test_large(folio)) {
                        folio_put(folio);
                        goto drop;
                }

                /*
                 * Move the inode on the list back to shrinklist if we failed
                 * to lock the page at this time.
                 *
                 * Waiting for the lock may lead to deadlock in the
                 * reclaim path.
                 */
                if (!folio_trylock(folio)) {
                        folio_put(folio);
                        goto move_back;
                }

                ret = split_folio(folio);
                folio_unlock(folio);
                folio_put(folio);

                /* If split failed move the inode on the list back to shrinklist */
                if (ret)
                        goto move_back;

                split++;
drop:
                list_del_init(&info->shrinklist);
                goto put;
move_back:
                /*
                 * Make sure the inode is either on the global list or deleted
                 * from any local list before iput() since it could be deleted
                 * in another thread once we put the inode (then the local list
                 * is corrupted).
                 */
                spin_lock(&sbinfo->shrinklist_lock);
                list_move(&info->shrinklist, &sbinfo->shrinklist);
                sbinfo->shrinklist_len++;
                spin_unlock(&sbinfo->shrinklist_lock);
put:
                iput(inode);
        }

        return split;
}

static long shmem_unused_huge_scan(struct super_block *sb,
                struct shrink_control *sc)
{
        struct shmem_sb_info *sbinfo = SHMEM_SB(sb);

        if (!READ_ONCE(sbinfo->shrinklist_len))
                return SHRINK_STOP;

        return shmem_unused_huge_shrink(sbinfo, sc, 0);
}

static long shmem_unused_huge_count(struct super_block *sb,
                struct shrink_control *sc)
{
        struct shmem_sb_info *sbinfo = SHMEM_SB(sb);
        return READ_ONCE(sbinfo->shrinklist_len);
}
#else /* !CONFIG_TRANSPARENT_HUGEPAGE */

#define shmem_huge SHMEM_HUGE_DENY

bool shmem_is_huge(struct vm_area_struct *vma, struct inode *inode,
                   pgoff_t index, bool shmem_huge_force)
{
        return false;
}

static unsigned long shmem_unused_huge_shrink(struct shmem_sb_info *sbinfo,
                struct shrink_control *sc, unsigned long nr_to_split)
{
        return 0;
}
#endif /* CONFIG_TRANSPARENT_HUGEPAGE */

/*
 * Like filemap_add_folio, but error if expected item has gone.
 */
static int shmem_add_to_page_cache(struct folio *folio,
                                   struct address_space *mapping,
                                   pgoff_t index, void *expected, gfp_t gfp,
                                   struct mm_struct *charge_mm)
{
        XA_STATE_ORDER(xas, &mapping->i_pages, index, folio_order(folio));
        long nr = folio_nr_pages(folio);
        int error;

        VM_BUG_ON_FOLIO(index != round_down(index, nr), folio);
        VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
        VM_BUG_ON_FOLIO(!folio_test_swapbacked(folio), folio);
        VM_BUG_ON(expected && folio_test_large(folio));

        folio_ref_add(folio, nr);
        folio->mapping = mapping;
        folio->index = index;

        if (!folio_test_swapcache(folio)) {
                error = mem_cgroup_charge(folio, charge_mm, gfp);
                if (error) {
                        if (folio_test_pmd_mappable(folio)) {
                                count_vm_event(THP_FILE_FALLBACK);
                                count_vm_event(THP_FILE_FALLBACK_CHARGE);
                        }
                        goto error;
                }
        }
        folio_throttle_swaprate(folio, gfp);

        do {
                xas_lock_irq(&xas);
                if (expected != xas_find_conflict(&xas)) {
                        xas_set_err(&xas, -EEXIST);
                        goto unlock;
                }
                if (expected && xas_find_conflict(&xas)) {
                        xas_set_err(&xas, -EEXIST);
                        goto unlock;
                }
                xas_store(&xas, folio);
                if (xas_error(&xas))
                        goto unlock;
                if (folio_test_pmd_mappable(folio)) {
                        count_vm_event(THP_FILE_ALLOC);
                        __lruvec_stat_mod_folio(folio, NR_SHMEM_THPS, nr);
                }
                mapping->nrpages += nr;
                __lruvec_stat_mod_folio(folio, NR_FILE_PAGES, nr);
                __lruvec_stat_mod_folio(folio, NR_SHMEM, nr);
unlock:
                xas_unlock_irq(&xas);
        } while (xas_nomem(&xas, gfp));

        if (xas_error(&xas)) {
                error = xas_error(&xas);
                goto error;
        }

        return 0;
error:
        folio->mapping = NULL;
        folio_ref_sub(folio, nr);
        return error;
}

/*
 * Like delete_from_page_cache, but substitutes swap for @folio.
 */
static void shmem_delete_from_page_cache(struct folio *folio, void *radswap)
{
        struct address_space *mapping = folio->mapping;
        long nr = folio_nr_pages(folio);
        int error;

        xa_lock_irq(&mapping->i_pages);
        error = shmem_replace_entry(mapping, folio->index, folio, radswap);
        folio->mapping = NULL;
        mapping->nrpages -= nr;
        __lruvec_stat_mod_folio(folio, NR_FILE_PAGES, -nr);
        __lruvec_stat_mod_folio(folio, NR_SHMEM, -nr);
        xa_unlock_irq(&mapping->i_pages);
        folio_put(folio);
        BUG_ON(error);
}

/*
 * Remove swap entry from page cache, free the swap and its page cache.
 */
static int shmem_free_swap(struct address_space *mapping,
                           pgoff_t index, void *radswap)
{
        void *old;

        old = xa_cmpxchg_irq(&mapping->i_pages, index, radswap, NULL, 0);
        if (old != radswap)
                return -ENOENT;
        free_swap_and_cache(radix_to_swp_entry(radswap));
        return 0;
}

/*
 * Determine (in bytes) how many of the shmem object's pages mapped by the
 * given offsets are swapped out.
 *
 * This is safe to call without i_rwsem or the i_pages lock thanks to RCU,
 * as long as the inode doesn't go away and racy results are not a problem.
 */
unsigned long shmem_partial_swap_usage(struct address_space *mapping,
                                                pgoff_t start, pgoff_t end)
{
        XA_STATE(xas, &mapping->i_pages, start);
        struct page *page;
        unsigned long swapped = 0;

        rcu_read_lock();
        xas_for_each(&xas, page, end - 1) {
                if (xas_retry(&xas, page))
                        continue;
                if (xa_is_value(page))
                        swapped++;

                if (need_resched()) {
                        xas_pause(&xas);
                        cond_resched_rcu();
                }
        }

        rcu_read_unlock();

        return swapped << PAGE_SHIFT;
}

/*
 * Determine (in bytes) how many of the shmem object's pages mapped by the
 * given vma is swapped out.
 *
 * This is safe to call without i_rwsem or the i_pages lock thanks to RCU,
 * as long as the inode doesn't go away and racy results are not a problem.
 */
unsigned long shmem_swap_usage(struct vm_area_struct *vma)
{
        struct inode *inode = file_inode(vma->vm_file);
        struct shmem_inode_info *info = SHMEM_I(inode);
        struct address_space *mapping = inode->i_mapping;
        unsigned long swapped;

        /* Be careful as we don't hold info->lock */
        swapped = READ_ONCE(info->swapped);

        /*
         * The easier cases are when the shmem object has nothing in swap, or
         * the vma maps it whole. Then we can simply use the stats that we
         * already track.
         */
        if (!swapped)
                return 0;

        if (!vma->vm_pgoff && vma->vm_end - vma->vm_start >= inode->i_size)
                return swapped << PAGE_SHIFT;

        /* Here comes the more involved part */
        return shmem_partial_swap_usage(mapping, vma->vm_pgoff,
                                        vma->vm_pgoff + vma_pages(vma));
}

/*
 * SysV IPC SHM_UNLOCK restore Unevictable pages to their evictable lists.
 */
void shmem_unlock_mapping(struct address_space *mapping)
{
        struct folio_batch fbatch;
        pgoff_t index = 0;

        folio_batch_init(&fbatch);
        /*
         * Minor point, but we might as well stop if someone else SHM_LOCKs it.
         */
        while (!mapping_unevictable(mapping) &&
               filemap_get_folios(mapping, &index, ~0UL, &fbatch)) {
                check_move_unevictable_folios(&fbatch);
                folio_batch_release(&fbatch);
                cond_resched();
        }
}

static struct folio *shmem_get_partial_folio(struct inode *inode, pgoff_t index)
{
        struct folio *folio;

        /*
         * At first avoid shmem_get_folio(,,,SGP_READ): that fails
         * beyond i_size, and reports fallocated pages as holes.
         */
        folio = __filemap_get_folio(inode->i_mapping, index,
                                        FGP_ENTRY | FGP_LOCK, 0);
        if (!xa_is_value(folio))
                return folio;
        /*
         * But read a page back from swap if any of it is within i_size
         * (although in some cases this is just a waste of time).
         */
        folio = NULL;
        shmem_get_folio(inode, index, &folio, SGP_READ);
        return folio;
}

/*
 * Remove range of pages and swap entries from page cache, and free them.
 * If !unfalloc, truncate or punch hole; if unfalloc, undo failed fallocate.
 */
static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend,
                                                                 bool unfalloc)
{
        struct address_space *mapping = inode->i_mapping;
        struct shmem_inode_info *info = SHMEM_I(inode);
        pgoff_t start = (lstart + PAGE_SIZE - 1) >> PAGE_SHIFT;
        pgoff_t end = (lend + 1) >> PAGE_SHIFT;
        struct folio_batch fbatch;
        pgoff_t indices[PAGEVEC_SIZE];
        struct folio *folio;
        bool same_folio;
        long nr_swaps_freed = 0;
        pgoff_t index;
        int i;

        if (lend == -1)
                end = -1;       /* unsigned, so actually very big */

        if (info->fallocend > start && info->fallocend <= end && !unfalloc)
                info->fallocend = start;

        folio_batch_init(&fbatch);
        index = start;
        while (index < end && find_lock_entries(mapping, &index, end - 1,
                        &fbatch, indices)) {
                for (i = 0; i < folio_batch_count(&fbatch); i++) {
                        folio = fbatch.folios[i];

                        if (xa_is_value(folio)) {
                                if (unfalloc)
                                        continue;
                                nr_swaps_freed += !shmem_free_swap(mapping,
                                                        indices[i], folio);
                                continue;
                        }

                        if (!unfalloc || !folio_test_uptodate(folio))
                                truncate_inode_folio(mapping, folio);
                        folio_unlock(folio);
                }
                folio_batch_remove_exceptionals(&fbatch);
                folio_batch_release(&fbatch);
                cond_resched();
        }

        same_folio = (lstart >> PAGE_SHIFT) == (lend >> PAGE_SHIFT);
        folio = shmem_get_partial_folio(inode, lstart >> PAGE_SHIFT);
        if (folio) {
                same_folio = lend < folio_pos(folio) + folio_size(folio);
                folio_mark_dirty(folio);
                if (!truncate_inode_partial_folio(folio, lstart, lend)) {
                        start = folio->index + folio_nr_pages(folio);
                        if (same_folio)
                                end = folio->index;
                }
                folio_unlock(folio);
                folio_put(folio);
                folio = NULL;
        }

        if (!same_folio)
                folio = shmem_get_partial_folio(inode, lend >> PAGE_SHIFT);
        if (folio) {
                folio_mark_dirty(folio);
                if (!truncate_inode_partial_folio(folio, lstart, lend))
                        end = folio->index;
                folio_unlock(folio);
                folio_put(folio);
        }

        index = start;
        while (index < end) {
                cond_resched();

                if (!find_get_entries(mapping, &index, end - 1, &fbatch,
                                indices)) {
                        /* If all gone or hole-punch or unfalloc, we're done */
                        if (index == start || end != -1)
                                break;
                        /* But if truncating, restart to make sure all gone */
                        index = start;
                        continue;
                }
                for (i = 0; i < folio_batch_count(&fbatch); i++) {
                        folio = fbatch.folios[i];

                        if (xa_is_value(folio)) {
                                if (unfalloc)
                                        continue;
                                if (shmem_free_swap(mapping, indices[i], folio)) {
                                        /* Swap was replaced by page: retry */
                                        index = indices[i];
                                        break;
                                }
                                nr_swaps_freed++;
                                continue;
                        }

                        folio_lock(folio);

                        if (!unfalloc || !folio_test_uptodate(folio)) {
                                if (folio_mapping(folio) != mapping) {
                                        /* Page was replaced by swap: retry */
                                        folio_unlock(folio);
                                        index = indices[i];
                                        break;
                                }
                                VM_BUG_ON_FOLIO(folio_test_writeback(folio),
                                                folio);
                                truncate_inode_folio(mapping, folio);
                        }
                        folio_unlock(folio);
                }
                folio_batch_remove_exceptionals(&fbatch);
                folio_batch_release(&fbatch);
        }

        spin_lock_irq(&info->lock);
        info->swapped -= nr_swaps_freed;
        shmem_recalc_inode(inode);
        spin_unlock_irq(&info->lock);
}

void shmem_truncate_range(struct inode *inode, loff_t lstart, loff_t lend)
{
        shmem_undo_range(inode, lstart, lend, false);
        inode->i_ctime = inode->i_mtime = current_time(inode);
        inode_inc_iversion(inode);
}
EXPORT_SYMBOL_GPL(shmem_truncate_range);

static int shmem_getattr(struct user_namespace *mnt_userns,
                         const struct path *path, struct kstat *stat,
                         u32 request_mask, unsigned int query_flags)
{
        struct inode *inode = path->dentry->d_inode;
        struct shmem_inode_info *info = SHMEM_I(inode);

        if (info->alloced - info->swapped != inode->i_mapping->nrpages) {
                spin_lock_irq(&info->lock);
                shmem_recalc_inode(inode);
                spin_unlock_irq(&info->lock);
        }
        if (info->fsflags & FS_APPEND_FL)
                stat->attributes |= STATX_ATTR_APPEND;
        if (info->fsflags & FS_IMMUTABLE_FL)
                stat->attributes |= STATX_ATTR_IMMUTABLE;
        if (info->fsflags & FS_NODUMP_FL)
                stat->attributes |= STATX_ATTR_NODUMP;
        stat->attributes_mask |= (STATX_ATTR_APPEND |
                        STATX_ATTR_IMMUTABLE |
                        STATX_ATTR_NODUMP);
        generic_fillattr(&init_user_ns, inode, stat);

        if (shmem_is_huge(NULL, inode, 0, false))
                stat->blksize = HPAGE_PMD_SIZE;

        if (request_mask & STATX_BTIME) {
                stat->result_mask |= STATX_BTIME;
                stat->btime.tv_sec = info->i_crtime.tv_sec;
                stat->btime.tv_nsec = info->i_crtime.tv_nsec;
        }

        return 0;
}

static int shmem_setattr(struct user_namespace *mnt_userns,
                         struct dentry *dentry, struct iattr *attr)
{
        struct inode *inode = d_inode(dentry);
        struct shmem_inode_info *info = SHMEM_I(inode);
        int error;
        bool update_mtime = false;
        bool update_ctime = true;

        error = setattr_prepare(&init_user_ns, dentry, attr);
        if (error)
                return error;

        if (S_ISREG(inode->i_mode) && (attr->ia_valid & ATTR_SIZE)) {
                loff_t oldsize = inode->i_size;
                loff_t newsize = attr->ia_size;

                /* protected by i_rwsem */
                if ((newsize < oldsize && (info->seals & F_SEAL_SHRINK)) ||
                    (newsize > oldsize && (info->seals & F_SEAL_GROW)))
                        return -EPERM;

                if (newsize != oldsize) {
                        error = shmem_reacct_size(SHMEM_I(inode)->flags,
                                        oldsize, newsize);
                        if (error)
                                return error;
                        i_size_write(inode, newsize);
                        update_mtime = true;
                } else {
                        update_ctime = false;
                }
                if (newsize <= oldsize) {
                        loff_t holebegin = round_up(newsize, PAGE_SIZE);
                        if (oldsize > holebegin)
                                unmap_mapping_range(inode->i_mapping,
                                                        holebegin, 0, 1);
                        if (info->alloced)
                                shmem_truncate_range(inode,
                                                        newsize, (loff_t)-1);
                        /* unmap again to remove racily COWed private pages */
                        if (oldsize > holebegin)
                                unmap_mapping_range(inode->i_mapping,
                                                        holebegin, 0, 1);
                }
        }

        setattr_copy(&init_user_ns, inode, attr);
        if (attr->ia_valid & ATTR_MODE)
                error = posix_acl_chmod(&init_user_ns, inode, inode->i_mode);
        if (!error && update_ctime) {
                inode->i_ctime = current_time(inode);
                if (update_mtime)
                        inode->i_mtime = inode->i_ctime;
                inode_inc_iversion(inode);
        }
        return error;
}

static void shmem_evict_inode(struct inode *inode)
{
        struct shmem_inode_info *info = SHMEM_I(inode);
        struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);

        if (shmem_mapping(inode->i_mapping)) {
                shmem_unacct_size(info->flags, inode->i_size);
                inode->i_size = 0;
                mapping_set_exiting(inode->i_mapping);
                shmem_truncate_range(inode, 0, (loff_t)-1);
                if (!list_empty(&info->shrinklist)) {
                        spin_lock(&sbinfo->shrinklist_lock);
                        if (!list_empty(&info->shrinklist)) {
                                list_del_init(&info->shrinklist);
                                sbinfo->shrinklist_len--;
                        }
                        spin_unlock(&sbinfo->shrinklist_lock);
                }
                while (!list_empty(&info->swaplist)) {
                        /* Wait while shmem_unuse() is scanning this inode... */
                        wait_var_event(&info->stop_eviction,
                                       !atomic_read(&info->stop_eviction));
                        mutex_lock(&shmem_swaplist_mutex);
                        /* ...but beware of the race if we peeked too early */
                        if (!atomic_read(&info->stop_eviction))
                                list_del_init(&info->swaplist);
                        mutex_unlock(&shmem_swaplist_mutex);
                }
        }

        simple_xattrs_free(&info->xattrs);
        WARN_ON(inode->i_blocks);
        shmem_free_inode(inode->i_sb);
        clear_inode(inode);
}

static int shmem_find_swap_entries(struct address_space *mapping,
                                   pgoff_t start, struct folio_batch *fbatch,
                                   pgoff_t *indices, unsigned int type)
{
        XA_STATE(xas, &mapping->i_pages, start);
        struct folio *folio;
        swp_entry_t entry;

        rcu_read_lock();
        xas_for_each(&xas, folio, ULONG_MAX) {
                if (xas_retry(&xas, folio))
                        continue;

                if (!xa_is_value(folio))
                        continue;

                entry = radix_to_swp_entry(folio);
                /*
                 * swapin error entries can be found in the mapping. But they're
                 * deliberately ignored here as we've done everything we can do.
                 */
                if (swp_type(entry) != type)
                        continue;

                indices[folio_batch_count(fbatch)] = xas.xa_index;
                if (!folio_batch_add(fbatch, folio))
                        break;

                if (need_resched()) {
                        xas_pause(&xas);
                        cond_resched_rcu();
                }
        }
        rcu_read_unlock();

        return xas.xa_index;
}

/*
 * Move the swapped pages for an inode to page cache. Returns the count
 * of pages swapped in, or the error in case of failure.
 */
static int shmem_unuse_swap_entries(struct inode *inode,
                struct folio_batch *fbatch, pgoff_t *indices)
{
        int i = 0;
        int ret = 0;
        int error = 0;
        struct address_space *mapping = inode->i_mapping;

        for (i = 0; i < folio_batch_count(fbatch); i++) {
                struct folio *folio = fbatch->folios[i];

                if (!xa_is_value(folio))
                        continue;
                error = shmem_swapin_folio(inode, indices[i],
                                          &folio, SGP_CACHE,
                                          mapping_gfp_mask(mapping),
                                          NULL, NULL);
                if (error == 0) {
                        folio_unlock(folio);
                        folio_put(folio);
                        ret++;
                }
                if (error == -ENOMEM)
                        break;
                error = 0;
        }
        return error ? error : ret;
}

/*
 * If swap found in inode, free it and move page from swapcache to filecache.
 */
static int shmem_unuse_inode(struct inode *inode, unsigned int type)
{
        struct address_space *mapping = inode->i_mapping;
        pgoff_t start = 0;
        struct folio_batch fbatch;
        pgoff_t indices[PAGEVEC_SIZE];
        int ret = 0;

        do {
                folio_batch_init(&fbatch);
                shmem_find_swap_entries(mapping, start, &fbatch, indices, type);
                if (folio_batch_count(&fbatch) == 0) {
                        ret = 0;
                        break;
                }

                ret = shmem_unuse_swap_entries(inode, &fbatch, indices);
                if (ret < 0)
                        break;

                start = indices[folio_batch_count(&fbatch) - 1];
        } while (true);

        return ret;
}

/*
 * Read all the shared memory data that resides in the swap
 * device 'type' back into memory, so the swap device can be
 * unused.
 */
int shmem_unuse(unsigned int type)
{
        struct shmem_inode_info *info, *next;
        int error = 0;

        if (list_empty(&shmem_swaplist))
                return 0;

        mutex_lock(&shmem_swaplist_mutex);
        list_for_each_entry_safe(info, next, &shmem_swaplist, swaplist) {
                if (!info->swapped) {
                        list_del_init(&info->swaplist);
                        continue;
                }
                /*
                 * Drop the swaplist mutex while searching the inode for swap;
                 * but before doing so, make sure shmem_evict_inode() will not
                 * remove placeholder inode from swaplist, nor let it be freed
                 * (igrab() would protect from unlink, but not from unmount).
                 */
                atomic_inc(&info->stop_eviction);
                mutex_unlock(&shmem_swaplist_mutex);

                error = shmem_unuse_inode(&info->vfs_inode, type);
                cond_resched();

                mutex_lock(&shmem_swaplist_mutex);
                next = list_next_entry(info, swaplist);
                if (!info->swapped)
                        list_del_init(&info->swaplist);
                if (atomic_dec_and_test(&info->stop_eviction))
                        wake_up_var(&info->stop_eviction);
                if (error)
                        break;
        }
        mutex_unlock(&shmem_swaplist_mutex);

        return error;
}

/*
 * Move the page from the page cache to the swap cache.
 */
static int shmem_writepage(struct page *page, struct writeback_control *wbc)
{
        struct folio *folio = page_folio(page);
        struct shmem_inode_info *info;
        struct address_space *mapping;
        struct inode *inode;
        swp_entry_t swap;
        pgoff_t index;

        /*
         * If /sys/kernel/mm/transparent_hugepage/shmem_enabled is "always" or
         * "force", drivers/gpu/drm/i915/gem/i915_gem_shmem.c gets huge pages,
         * and its shmem_writeback() needs them to be split when swapping.
         */
        if (folio_test_large(folio)) {
                /* Ensure the subpages are still dirty */
                folio_test_set_dirty(folio);
                if (split_huge_page(page) < 0)
                        goto redirty;
                folio = page_folio(page);
                folio_clear_dirty(folio);
        }

        BUG_ON(!folio_test_locked(folio));
        mapping = folio->mapping;
        index = folio->index;
        inode = mapping->host;
        info = SHMEM_I(inode);
        if (info->flags & VM_LOCKED)
                goto redirty;
        if (!total_swap_pages)
                goto redirty;

        /*
         * Our capabilities prevent regular writeback or sync from ever calling
         * shmem_writepage; but a stacking filesystem might use ->writepage of
         * its underlying filesystem, in which case tmpfs should write out to
         * swap only in response to memory pressure, and not for the writeback
         * threads or sync.
         */
        if (!wbc->for_reclaim) {
                WARN_ON_ONCE(1);        /* Still happens? Tell us about it! */
                goto redirty;
        }

        /*
         * This is somewhat ridiculous, but without plumbing a SWAP_MAP_FALLOC
         * value into swapfile.c, the only way we can correctly account for a
         * fallocated folio arriving here is now to initialize it and write it.
         *
         * That's okay for a folio already fallocated earlier, but if we have
         * not yet completed the fallocation, then (a) we want to keep track
         * of this folio in case we have to undo it, and (b) it may not be a
         * good idea to continue anyway, once we're pushing into swap.  So
         * reactivate the folio, and let shmem_fallocate() quit when too many.
         */
        if (!folio_test_uptodate(folio)) {
                if (inode->i_private) {
                        struct shmem_falloc *shmem_falloc;
                        spin_lock(&inode->i_lock);
                        shmem_falloc = inode->i_private;
                        if (shmem_falloc &&
                            !shmem_falloc->waitq &&
                            index >= shmem_falloc->start &&
                            index < shmem_falloc->next)
                                shmem_falloc->nr_unswapped++;
                        else
                                shmem_falloc = NULL;
                        spin_unlock(&inode->i_lock);
                        if (shmem_falloc)
                                goto redirty;
                }
                folio_zero_range(folio, 0, folio_size(folio));
                flush_dcache_folio(folio);
                folio_mark_uptodate(folio);
        }

        swap = folio_alloc_swap(folio);
        if (!swap.val)
                goto redirty;

        /*
         * Add inode to shmem_unuse()'s list of swapped-out inodes,
         * if it's not already there.  Do it now before the folio is
         * moved to swap cache, when its pagelock no longer protects
         * the inode from eviction.  But don't unlock the mutex until
         * we've incremented swapped, because shmem_unuse_inode() will
         * prune a !swapped inode from the swaplist under this mutex.
         */
        mutex_lock(&shmem_swaplist_mutex);
        if (list_empty(&info->swaplist))
                list_add(&info->swaplist, &shmem_swaplist);

        if (add_to_swap_cache(folio, swap,
                        __GFP_HIGH | __GFP_NOMEMALLOC | __GFP_NOWARN,
                        NULL) == 0) {
                spin_lock_irq(&info->lock);
                shmem_recalc_inode(inode);
                info->swapped++;
                spin_unlock_irq(&info->lock);

                swap_shmem_alloc(swap);
                shmem_delete_from_page_cache(folio, swp_to_radix_entry(swap));

                mutex_unlock(&shmem_swaplist_mutex);
                BUG_ON(folio_mapped(folio));
                swap_writepage(&folio->page, wbc);
                return 0;
        }

        mutex_unlock(&shmem_swaplist_mutex);
        put_swap_folio(folio, swap);
redirty:
        folio_mark_dirty(folio);
        if (wbc->for_reclaim)
                return AOP_WRITEPAGE_ACTIVATE;  /* Return with folio locked */
        folio_unlock(folio);
        return 0;
}

#if defined(CONFIG_NUMA) && defined(CONFIG_TMPFS)
static void shmem_show_mpol(struct seq_file *seq, struct mempolicy *mpol)
{
        char buffer[64];

        if (!mpol || mpol->mode == MPOL_DEFAULT)
                return;         /* show nothing */

        mpol_to_str(buffer, sizeof(buffer), mpol);

        seq_printf(seq, ",mpol=%s", buffer);
}

static struct mempolicy *shmem_get_sbmpol(struct shmem_sb_info *sbinfo)
{
        struct mempolicy *mpol = NULL;
        if (sbinfo->mpol) {
                raw_spin_lock(&sbinfo->stat_lock);      /* prevent replace/use races */
                mpol = sbinfo->mpol;
                mpol_get(mpol);
                raw_spin_unlock(&sbinfo->stat_lock);
        }
        return mpol;
}
#else /* !CONFIG_NUMA || !CONFIG_TMPFS */
static inline void shmem_show_mpol(struct seq_file *seq, struct mempolicy *mpol)
{
}
static inline struct mempolicy *shmem_get_sbmpol(struct shmem_sb_info *sbinfo)
{
        return NULL;
}
#endif /* CONFIG_NUMA && CONFIG_TMPFS */
#ifndef CONFIG_NUMA
#define vm_policy vm_private_data
#endif

static void shmem_pseudo_vma_init(struct vm_area_struct *vma,
                struct shmem_inode_info *info, pgoff_t index)
{
        /* Create a pseudo vma that just contains the policy */
        vma_init(vma, NULL);
        /* Bias interleave by inode number to distribute better across nodes */
        vma->vm_pgoff = index + info->vfs_inode.i_ino;
        vma->vm_policy = mpol_shared_policy_lookup(&info->policy, index);
}

static void shmem_pseudo_vma_destroy(struct vm_area_struct *vma)
{
        /* Drop reference taken by mpol_shared_policy_lookup() */
        mpol_cond_put(vma->vm_policy);
}

static struct folio *shmem_swapin(swp_entry_t swap, gfp_t gfp,
                        struct shmem_inode_info *info, pgoff_t index)
{
        struct vm_area_struct pvma;
        struct page *page;
        struct vm_fault vmf = {
                .vma = &pvma,
        };

        shmem_pseudo_vma_init(&pvma, info, index);
        page = swap_cluster_readahead(swap, gfp, &vmf);
        shmem_pseudo_vma_destroy(&pvma);

        if (!page)
                return NULL;
        return page_folio(page);
}

/*
 * Make sure huge_gfp is always more limited than limit_gfp.
 * Some of the flags set permissions, while others set limitations.
 */
static gfp_t limit_gfp_mask(gfp_t huge_gfp, gfp_t limit_gfp)
{
        gfp_t allowflags = __GFP_IO | __GFP_FS | __GFP_RECLAIM;
        gfp_t denyflags = __GFP_NOWARN | __GFP_NORETRY;
        gfp_t zoneflags = limit_gfp & GFP_ZONEMASK;
        gfp_t result = huge_gfp & ~(allowflags | GFP_ZONEMASK);

        /* Allow allocations only from the originally specified zones. */
        result |= zoneflags;

        /*
         * Minimize the result gfp by taking the union with the deny flags,
         * and the intersection of the allow flags.
         */
        result |= (limit_gfp & denyflags);
        result |= (huge_gfp & limit_gfp) & allowflags;

        return result;
}

static struct folio *shmem_alloc_hugefolio(gfp_t gfp,
                struct shmem_inode_info *info, pgoff_t index)
{
        struct vm_area_struct pvma;
        struct address_space *mapping = info->vfs_inode.i_mapping;
        pgoff_t hindex;
        struct folio *folio;

        hindex = round_down(index, HPAGE_PMD_NR);
        if (xa_find(&mapping->i_pages, &hindex, hindex + HPAGE_PMD_NR - 1,
                                                                XA_PRESENT))
                return NULL;

        shmem_pseudo_vma_init(&pvma, info, hindex);
        folio = vma_alloc_folio(gfp, HPAGE_PMD_ORDER, &pvma, 0, true);
        shmem_pseudo_vma_destroy(&pvma);
        if (!folio)
                count_vm_event(THP_FILE_FALLBACK);
        return folio;
}

static struct folio *shmem_alloc_folio(gfp_t gfp,
                        struct shmem_inode_info *info, pgoff_t index)
{
        struct vm_area_struct pvma;
        struct folio *folio;

        shmem_pseudo_vma_init(&pvma, info, index);
        folio = vma_alloc_folio(gfp, 0, &pvma, 0, false);
        shmem_pseudo_vma_destroy(&pvma);

        return folio;
}

static struct folio *shmem_alloc_and_acct_folio(gfp_t gfp, struct inode *inode,
                pgoff_t index, bool huge)
{
        struct shmem_inode_info *info = SHMEM_I(inode);
        struct folio *folio;
        int nr;
        int err = -ENOSPC;

        if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE))
                huge = false;
        nr = huge ? HPAGE_PMD_NR : 1;

        if (!shmem_inode_acct_block(inode, nr))
                goto failed;

        if (huge)
                folio = shmem_alloc_hugefolio(gfp, info, index);
        else
                folio = shmem_alloc_folio(gfp, info, index);
        if (folio) {
                __folio_set_locked(folio);
                __folio_set_swapbacked(folio);
                return folio;
        }

        err = -ENOMEM;
        shmem_inode_unacct_blocks(inode, nr);
failed:
        return ERR_PTR(err);
}

/*
 * When a page is moved from swapcache to shmem filecache (either by the
 * usual swapin of shmem_get_folio_gfp(), or by the less common swapoff of
 * shmem_unuse_inode()), it may have been read in earlier from swap, in
 * ignorance of the mapping it belongs to.  If that mapping has special
 * constraints (like the gma500 GEM driver, which requires RAM below 4GB),
 * we may need to copy to a suitable page before moving to filecache.
 *
 * In a future release, this may well be extended to respect cpuset and
 * NUMA mempolicy, and applied also to anonymous pages in do_swap_page();
 * but for now it is a simple matter of zone.
 */
static bool shmem_should_replace_folio(struct folio *folio, gfp_t gfp)
{
        return folio_zonenum(folio) > gfp_zone(gfp);
}

static int shmem_replace_folio(struct folio **foliop, gfp_t gfp,
                                struct shmem_inode_info *info, pgoff_t index)
{
        struct folio *old, *new;
        struct address_space *swap_mapping;
        swp_entry_t entry;
        pgoff_t swap_index;
        int error;

        old = *foliop;
        entry = folio_swap_entry(old);
        swap_index = swp_offset(entry);
        swap_mapping = swap_address_space(entry);

        /*
         * We have arrived here because our zones are constrained, so don't
         * limit chance of success by further cpuset and node constraints.
         */
        gfp &= ~GFP_CONSTRAINT_MASK;
        VM_BUG_ON_FOLIO(folio_test_large(old), old);
        new = shmem_alloc_folio(gfp, info, index);
        if (!new)
                return -ENOMEM;

        folio_get(new);
        folio_copy(new, old);
        flush_dcache_folio(new);

        __folio_set_locked(new);
        __folio_set_swapbacked(new);
        folio_mark_uptodate(new);
        folio_set_swap_entry(new, entry);
        folio_set_swapcache(new);

        /*
         * Our caller will very soon move newpage out of swapcache, but it's
         * a nice clean interface for us to replace oldpage by newpage there.
         */
        xa_lock_irq(&swap_mapping->i_pages);
        error = shmem_replace_entry(swap_mapping, swap_index, old, new);
        if (!error) {
                mem_cgroup_migrate(old, new);
                __lruvec_stat_mod_folio(new, NR_FILE_PAGES, 1);
                __lruvec_stat_mod_folio(new, NR_SHMEM, 1);
                __lruvec_stat_mod_folio(old, NR_FILE_PAGES, -1);
                __lruvec_stat_mod_folio(old, NR_SHMEM, -1);
        }
        xa_unlock_irq(&swap_mapping->i_pages);

        if (unlikely(error)) {
                /*
                 * Is this possible?  I think not, now that our callers check
                 * both PageSwapCache and page_private after getting page lock;
                 * but be defensive.  Reverse old to newpage for clear and free.
                 */
                old = new;
        } else {
                folio_add_lru(new);
                *foliop = new;
        }

        folio_clear_swapcache(old);
        old->private = NULL;

        folio_unlock(old);
        folio_put_refs(old, 2);
        return error;
}

static void shmem_set_folio_swapin_error(struct inode *inode, pgoff_t index,
                                         struct folio *folio, swp_entry_t swap)
{
        struct address_space *mapping = inode->i_mapping;
        struct shmem_inode_info *info = SHMEM_I(inode);
        swp_entry_t swapin_error;
        void *old;

        swapin_error = make_swapin_error_entry();
        old = xa_cmpxchg_irq(&mapping->i_pages, index,
                             swp_to_radix_entry(swap),
                             swp_to_radix_entry(swapin_error), 0);
        if (old != swp_to_radix_entry(swap))
                return;

        folio_wait_writeback(folio);
        delete_from_swap_cache(folio);
        spin_lock_irq(&info->lock);
        /*
         * Don't treat swapin error folio as alloced. Otherwise inode->i_blocks won't
         * be 0 when inode is released and thus trigger WARN_ON(inode->i_blocks) in
         * shmem_evict_inode.
         */
        info->alloced--;
        info->swapped--;
        shmem_recalc_inode(inode);
        spin_unlock_irq(&info->lock);
        swap_free(swap);
}

/*
 * Swap in the folio pointed to by *foliop.
 * Caller has to make sure that *foliop contains a valid swapped folio.
 * Returns 0 and the folio in foliop if success. On failure, returns the
 * error code and NULL in *foliop.
 */
static int shmem_swapin_folio(struct inode *inode, pgoff_t index,
                             struct folio **foliop, enum sgp_type sgp,
                             gfp_t gfp, struct vm_area_struct *vma,
                             vm_fault_t *fault_type)
{
        struct address_space *mapping = inode->i_mapping;
        struct shmem_inode_info *info = SHMEM_I(inode);
        struct mm_struct *charge_mm = vma ? vma->vm_mm : NULL;
        struct folio *folio = NULL;
        swp_entry_t swap;
        int error;

        VM_BUG_ON(!*foliop || !xa_is_value(*foliop));
        swap = radix_to_swp_entry(*foliop);
        *foliop = NULL;

        if (is_swapin_error_entry(swap))
                return -EIO;

        /* Look it up and read it in.. */
        folio = swap_cache_get_folio(swap, NULL, 0);
        if (!folio) {
                /* Or update major stats only when swapin succeeds?? */
                if (fault_type) {
                        *fault_type |= VM_FAULT_MAJOR;
                        count_vm_event(PGMAJFAULT);
                        count_memcg_event_mm(charge_mm, PGMAJFAULT);
                }
                /* Here we actually start the io */
                folio = shmem_swapin(swap, gfp, info, index);
                if (!folio) {
                        error = -ENOMEM;
                        goto failed;
                }
        }

        /* We have to do this with folio locked to prevent races */
        folio_lock(folio);
        if (!folio_test_swapcache(folio) ||
            folio_swap_entry(folio).val != swap.val ||
            !shmem_confirm_swap(mapping, index, swap)) {
                error = -EEXIST;
                goto unlock;
        }
        if (!folio_test_uptodate(folio)) {
                error = -EIO;
                goto failed;
        }
        folio_wait_writeback(folio);

        /*
         * Some architectures may have to restore extra metadata to the
         * folio after reading from swap.
         */
        arch_swap_restore(swap, folio);

        if (shmem_should_replace_folio(folio, gfp)) {
                error = shmem_replace_folio(&folio, gfp, info, index);
                if (error)
                        goto failed;
        }

        error = shmem_add_to_page_cache(folio, mapping, index,
                                        swp_to_radix_entry(swap), gfp,
                                        charge_mm);
        if (error)
                goto failed;

        spin_lock_irq(&info->lock);
        info->swapped--;
        shmem_recalc_inode(inode);
        spin_unlock_irq(&info->lock);

        if (sgp == SGP_WRITE)
                folio_mark_accessed(folio);

        delete_from_swap_cache(folio);
        folio_mark_dirty(folio);
        swap_free(swap);

        *foliop = folio;
        return 0;
failed:
        if (!shmem_confirm_swap(mapping, index, swap))
                error = -EEXIST;
        if (error == -EIO)
                shmem_set_folio_swapin_error(inode, index, folio, swap);
unlock:
        if (folio) {
                folio_unlock(folio);
                folio_put(folio);
        }

        return error;
}

/*
 * shmem_get_folio_gfp - find page in cache, or get from swap, or allocate
 *
 * If we allocate a new one we do not mark it dirty. That's up to the
 * vm. If we swap it in we mark it dirty since we also free the swap
 * entry since a page cannot live in both the swap and page cache.
 *
 * vma, vmf, and fault_type are only supplied by shmem_fault:
 * otherwise they are NULL.
 */
static int shmem_get_folio_gfp(struct inode *inode, pgoff_t index,
                struct folio **foliop, enum sgp_type sgp, gfp_t gfp,
                struct vm_area_struct *vma, struct vm_fault *vmf,
                vm_fault_t *fault_type)
{
        struct address_space *mapping = inode->i_mapping;
        struct shmem_inode_info *info = SHMEM_I(inode);
        struct shmem_sb_info *sbinfo;
        struct mm_struct *charge_mm;
        struct folio *folio;
        pgoff_t hindex;
        gfp_t huge_gfp;
        int error;
        int once = 0;
        int alloced = 0;

        if (index > (MAX_LFS_FILESIZE >> PAGE_SHIFT))
                return -EFBIG;
repeat:
        if (sgp <= SGP_CACHE &&
            ((loff_t)index << PAGE_SHIFT) >= i_size_read(inode)) {
                return -EINVAL;
        }

        sbinfo = SHMEM_SB(inode->i_sb);
        charge_mm = vma ? vma->vm_mm : NULL;

        folio = __filemap_get_folio(mapping, index, FGP_ENTRY | FGP_LOCK, 0);
        if (folio && vma && userfaultfd_minor(vma)) {
                if (!xa_is_value(folio)) {
                        folio_unlock(folio);
                        folio_put(folio);
                }
                *fault_type = handle_userfault(vmf, VM_UFFD_MINOR);
                return 0;
        }

        if (xa_is_value(folio)) {
                error = shmem_swapin_folio(inode, index, &folio,
                                          sgp, gfp, vma, fault_type);
                if (error == -EEXIST)
                        goto repeat;

                *foliop = folio;
                return error;
        }

        if (folio) {
                if (sgp == SGP_WRITE)
                        folio_mark_accessed(folio);
                if (folio_test_uptodate(folio))
                        goto out;
                /* fallocated folio */
                if (sgp != SGP_READ)
                        goto clear;
                folio_unlock(folio);
                folio_put(folio);
        }

        /*
         * SGP_READ: succeed on hole, with NULL folio, letting caller zero.
         * SGP_NOALLOC: fail on hole, with NULL folio, letting caller fail.
         */
        *foliop = NULL;
        if (sgp == SGP_READ)
                return 0;
        if (sgp == SGP_NOALLOC)
                return -ENOENT;

        /*
         * Fast cache lookup and swap lookup did not find it: allocate.
         */

        if (vma && userfaultfd_missing(vma)) {
                *fault_type = handle_userfault(vmf, VM_UFFD_MISSING);
                return 0;
        }

        if (!shmem_is_huge(vma, inode, index, false))
                goto alloc_nohuge;

        huge_gfp = vma_thp_gfp_mask(vma);
        huge_gfp = limit_gfp_mask(huge_gfp, gfp);
        folio = shmem_alloc_and_acct_folio(huge_gfp, inode, index, true);
        if (IS_ERR(folio)) {
alloc_nohuge:
                folio = shmem_alloc_and_acct_folio(gfp, inode, index, false);
        }
        if (IS_ERR(folio)) {
                int retry = 5;

                error = PTR_ERR(folio);
                folio = NULL;
                if (error != -ENOSPC)
                        goto unlock;
                /*
                 * Try to reclaim some space by splitting a large folio
                 * beyond i_size on the filesystem.
                 */
                while (retry--) {
                        int ret;

                        ret = shmem_unused_huge_shrink(sbinfo, NULL, 1);
                        if (ret == SHRINK_STOP)
                                break;
                        if (ret)
                                goto alloc_nohuge;
                }
                goto unlock;
        }

        hindex = round_down(index, folio_nr_pages(folio));

        if (sgp == SGP_WRITE)
                __folio_set_referenced(folio);

        error = shmem_add_to_page_cache(folio, mapping, hindex,
                                        NULL, gfp & GFP_RECLAIM_MASK,
                                        charge_mm);
        if (error)
                goto unacct;
        folio_add_lru(folio);

        spin_lock_irq(&info->lock);
        info->alloced += folio_nr_pages(folio);
        inode->i_blocks += (blkcnt_t)BLOCKS_PER_PAGE << folio_order(folio);
        shmem_recalc_inode(inode);
        spin_unlock_irq(&info->lock);
        alloced = true;

        if (folio_test_pmd_mappable(folio) &&
            DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE) <
                                        folio_next_index(folio) - 1) {
                /*
                 * Part of the large folio is beyond i_size: subject
                 * to shrink under memory pressure.
                 */
                spin_lock(&sbinfo->shrinklist_lock);
                /*
                 * _careful to defend against unlocked access to
                 * ->shrink_list in shmem_unused_huge_shrink()
                 */
                if (list_empty_careful(&info->shrinklist)) {
                        list_add_tail(&info->shrinklist,
                                      &sbinfo->shrinklist);
                        sbinfo->shrinklist_len++;
                }
                spin_unlock(&sbinfo->shrinklist_lock);
        }

        /*
         * Let SGP_FALLOC use the SGP_WRITE optimization on a new folio.
         */
        if (sgp == SGP_FALLOC)
                sgp = SGP_WRITE;
clear:
        /*
         * Let SGP_WRITE caller clear ends if write does not fill folio;
         * but SGP_FALLOC on a folio fallocated earlier must initialize
         * it now, lest undo on failure cancel our earlier guarantee.
         */
        if (sgp != SGP_WRITE && !folio_test_uptodate(folio)) {
                long i, n = folio_nr_pages(folio);

                for (i = 0; i < n; i++)
                        clear_highpage(folio_page(folio, i));
                flush_dcache_folio(folio);
                folio_mark_uptodate(folio);
        }

        /* Perhaps the file has been truncated since we checked */
        if (sgp <= SGP_CACHE &&
            ((loff_t)index << PAGE_SHIFT) >= i_size_read(inode)) {
                if (alloced) {
                        folio_clear_dirty(folio);
                        filemap_remove_folio(folio);
                        spin_lock_irq(&info->lock);
                        shmem_recalc_inode(inode);
                        spin_unlock_irq(&info->lock);
                }
                error = -EINVAL;
                goto unlock;
        }
out:
        *foliop = folio;
        return 0;

        /*
         * Error recovery.
         */
unacct:
        shmem_inode_unacct_blocks(inode, folio_nr_pages(folio));

        if (folio_test_large(folio)) {
                folio_unlock(folio);
                folio_put(folio);
                goto alloc_nohuge;
        }
unlock:
        if (folio) {
                folio_unlock(folio);
                folio_put(folio);
        }
        if (error == -ENOSPC && !once++) {
                spin_lock_irq(&info->lock);
                shmem_recalc_inode(inode);
                spin_unlock_irq(&info->lock);
                goto repeat;
        }
        if (error == -EEXIST)
                goto repeat;
        return error;
}

int shmem_get_folio(struct inode *inode, pgoff_t index, struct folio **foliop,
                enum sgp_type sgp)
{
        return shmem_get_folio_gfp(inode, index, foliop, sgp,
                        mapping_gfp_mask(inode->i_mapping), NULL, NULL, NULL);
}

/*
 * This is like autoremove_wake_function, but it removes the wait queue
 * entry unconditionally - even if something else had already woken the
 * target.
 */
static int synchronous_wake_function(wait_queue_entry_t *wait, unsigned mode, int sync, void *key)
{
        int ret = default_wake_function(wait, mode, sync, key);
        list_del_init(&wait->entry);
        return ret;
}

static vm_fault_t shmem_fault(struct vm_fault *vmf)
{
        struct vm_area_struct *vma = vmf->vma;
        struct inode *inode = file_inode(vma->vm_file);
        gfp_t gfp = mapping_gfp_mask(inode->i_mapping);
        struct folio *folio = NULL;
        int err;
        vm_fault_t ret = VM_FAULT_LOCKED;

        /*
         * Trinity finds that probing a hole which tmpfs is punching can
         * prevent the hole-punch from ever completing: which in turn
         * locks writers out with its hold on i_rwsem.  So refrain from
         * faulting pages into the hole while it's being punched.  Although
         * shmem_undo_range() does remove the additions, it may be unable to
         * keep up, as each new page needs its own unmap_mapping_range() call,
         * and the i_mmap tree grows ever slower to scan if new vmas are added.
         *
         * It does not matter if we sometimes reach this check just before the
         * hole-punch begins, so that one fault then races with the punch:
         * we just need to make racing faults a rare case.
         *
         * The implementation below would be much simpler if we just used a
         * standard mutex or completion: but we cannot take i_rwsem in fault,
         * and bloating every shmem inode for this unlikely case would be sad.
         */
        if (unlikely(inode->i_private)) {
                struct shmem_falloc *shmem_falloc;

                spin_lock(&inode->i_lock);
                shmem_falloc = inode->i_private;
                if (shmem_falloc &&
                    shmem_falloc->waitq &&
                    vmf->pgoff >= shmem_falloc->start &&
                    vmf->pgoff < shmem_falloc->next) {
                        struct file *fpin;
                        wait_queue_head_t *shmem_falloc_waitq;
                        DEFINE_WAIT_FUNC(shmem_fault_wait, synchronous_wake_function);

                        ret = VM_FAULT_NOPAGE;
                        fpin = maybe_unlock_mmap_for_io(vmf, NULL);
                        if (fpin)
                                ret = VM_FAULT_RETRY;

                        shmem_falloc_waitq = shmem_falloc->waitq;
                        prepare_to_wait(shmem_falloc_waitq, &shmem_fault_wait,
                                        TASK_UNINTERRUPTIBLE);
                        spin_unlock(&inode->i_lock);
                        schedule();

                        /*
                         * shmem_falloc_waitq points into the shmem_fallocate()
                         * stack of the hole-punching task: shmem_falloc_waitq
                         * is usually invalid by the time we reach here, but
                         * finish_wait() does not dereference it in that case;
                         * though i_lock needed lest racing with wake_up_all().
                         */
                        spin_lock(&inode->i_lock);
                        finish_wait(shmem_falloc_waitq, &shmem_fault_wait);
                        spin_unlock(&inode->i_lock);

                        if (fpin)
                                fput(fpin);
                        return ret;
                }
                spin_unlock(&inode->i_lock);
        }

        err = shmem_get_folio_gfp(inode, vmf->pgoff, &folio, SGP_CACHE,
                                  gfp, vma, vmf, &ret);
        if (err)
                return vmf_error(err);
        if (folio)
                vmf->page = folio_file_page(folio, vmf->pgoff);
        return ret;
}

unsigned long shmem_get_unmapped_area(struct file *file,
                                      unsigned long uaddr, unsigned long len,
                                      unsigned long pgoff, unsigned long flags)
{
        unsigned long (*get_area)(struct file *,
                unsigned long, unsigned long, unsigned long, unsigned long);
        unsigned long addr;
        unsigned long offset;
        unsigned long inflated_len;
        unsigned long inflated_addr;
        unsigned long inflated_offset;

        if (len > TASK_SIZE)
                return -ENOMEM;

        get_area = current->mm->get_unmapped_area;
        addr = get_area(file, uaddr, len, pgoff, flags);

        if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE))
                return addr;
        if (IS_ERR_VALUE(addr))
                return addr;
        if (addr & ~PAGE_MASK)
                return addr;
        if (addr > TASK_SIZE - len)
                return addr;

        if (shmem_huge == SHMEM_HUGE_DENY)
                return addr;
        if (len < HPAGE_PMD_SIZE)
                return addr;
        if (flags & MAP_FIXED)
                return addr;
        /*
         * Our priority is to support MAP_SHARED mapped hugely;
         * and support MAP_PRIVATE mapped hugely too, until it is COWed.
         * But if caller specified an address hint and we allocated area there
         * successfully, respect that as before.
         */
        if (uaddr == addr)
                return addr;

        if (shmem_huge != SHMEM_HUGE_FORCE) {
                struct super_block *sb;

                if (file) {
                        VM_BUG_ON(file->f_op != &shmem_file_operations);
                        sb = file_inode(file)->i_sb;
                } else {
                        /*
                         * Called directly from mm/mmap.c, or drivers/char/mem.c
                         * for "/dev/zero", to create a shared anonymous object.
                         */
                        if (IS_ERR(shm_mnt))
                                return addr;
                        sb = shm_mnt->mnt_sb;
                }
                if (SHMEM_SB(sb)->huge == SHMEM_HUGE_NEVER)
                        return addr;
        }

        offset = (pgoff << PAGE_SHIFT) & (HPAGE_PMD_SIZE-1);
        if (offset && offset + len < 2 * HPAGE_PMD_SIZE)
                return addr;
        if ((addr & (HPAGE_PMD_SIZE-1)) == offset)
                return addr;

        inflated_len = len + HPAGE_PMD_SIZE - PAGE_SIZE;
        if (inflated_len > TASK_SIZE)
                return addr;
        if (inflated_len < len)
                return addr;

        inflated_addr = get_area(NULL, uaddr, inflated_len, 0, flags);
        if (IS_ERR_VALUE(inflated_addr))
                return addr;
        if (inflated_addr & ~PAGE_MASK)
                return addr;

        inflated_offset = inflated_addr & (HPAGE_PMD_SIZE-1);
        inflated_addr += offset - inflated_offset;
        if (inflated_offset > offset)
                inflated_addr += HPAGE_PMD_SIZE;

        if (inflated_addr > TASK_SIZE - len)
                return addr;
        return inflated_addr;
}

#ifdef CONFIG_NUMA
static int shmem_set_policy(struct vm_area_struct *vma, struct mempolicy *mpol)
{
        struct inode *inode = file_inode(vma->vm_file);
        return mpol_set_shared_policy(&SHMEM_I(inode)->policy, vma, mpol);
}

static struct mempolicy *shmem_get_policy(struct vm_area_struct *vma,
                                          unsigned long addr)
{
        struct inode *inode = file_inode(vma->vm_file);
        pgoff_t index;

        index = ((addr - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
        return mpol_shared_policy_lookup(&SHMEM_I(inode)->policy, index);
}
#endif

int shmem_lock(struct file *file, int lock, struct ucounts *ucounts)
{
        struct inode *inode = file_inode(file);
        struct shmem_inode_info *info = SHMEM_I(inode);
        int retval = -ENOMEM;

        /*
         * What serializes the accesses to info->flags?
         * ipc_lock_object() when called from shmctl_do_lock(),
         * no serialization needed when called from shm_destroy().
         */
        if (lock && !(info->flags & VM_LOCKED)) {
                if (!user_shm_lock(inode->i_size, ucounts))
                        goto out_nomem;
                info->flags |= VM_LOCKED;
                mapping_set_unevictable(file->f_mapping);
        }
        if (!lock && (info->flags & VM_LOCKED) && ucounts) {
                user_shm_unlock(inode->i_size, ucounts);
                info->flags &= ~VM_LOCKED;
                mapping_clear_unevictable(file->f_mapping);
        }
        retval = 0;

out_nomem:
        return retval;
}

static int shmem_mmap(struct file *file, struct vm_area_struct *vma)
{
        struct shmem_inode_info *info = SHMEM_I(file_inode(file));
        int ret;

        ret = seal_check_future_write(info->seals, vma);
        if (ret)
                return ret;

        /* arm64 - allow memory tagging on RAM-based files */
        vma->vm_flags |= VM_MTE_ALLOWED;

        file_accessed(file);
        vma->vm_ops = &shmem_vm_ops;
        return 0;
}

#ifdef CONFIG_TMPFS_XATTR
static int shmem_initxattrs(struct inode *, const struct xattr *, void *);

/*
 * chattr's fsflags are unrelated to extended attributes,
 * but tmpfs has chosen to enable them under the same config option.
 */
static void shmem_set_inode_flags(struct inode *inode, unsigned int fsflags)
{
        unsigned int i_flags = 0;

        if (fsflags & FS_NOATIME_FL)
                i_flags |= S_NOATIME;
        if (fsflags & FS_APPEND_FL)
                i_flags |= S_APPEND;
        if (fsflags & FS_IMMUTABLE_FL)
                i_flags |= S_IMMUTABLE;
        /*
         * But FS_NODUMP_FL does not require any action in i_flags.
         */
        inode_set_flags(inode, i_flags, S_NOATIME | S_APPEND | S_IMMUTABLE);
}
#else
static void shmem_set_inode_flags(struct inode *inode, unsigned int fsflags)
{
}
#define shmem_initxattrs NULL
#endif

static struct inode *shmem_get_inode(struct super_block *sb, struct inode *dir,
                                     umode_t mode, dev_t dev, unsigned long flags)
{
        struct inode *inode;
        struct shmem_inode_info *info;
        struct shmem_sb_info *sbinfo = SHMEM_SB(sb);
        ino_t ino;

        if (shmem_reserve_inode(sb, &ino))
                return NULL;

        inode = new_inode(sb);
        if (inode) {
                inode->i_ino = ino;
                inode_init_owner(&init_user_ns, inode, dir, mode);
                inode->i_blocks = 0;
                inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode);
                inode->i_generation = get_random_u32();
                info = SHMEM_I(inode);
                memset(info, 0, (char *)inode - (char *)info);
                spin_lock_init(&info->lock);
                atomic_set(&info->stop_eviction, 0);
                info->seals = F_SEAL_SEAL;
                info->flags = flags & VM_NORESERVE;
                info->i_crtime = inode->i_mtime;
                info->fsflags = (dir == NULL) ? 0 :
                        SHMEM_I(dir)->fsflags & SHMEM_FL_INHERITED;
                if (info->fsflags)
                        shmem_set_inode_flags(inode, info->fsflags);
                INIT_LIST_HEAD(&info->shrinklist);
                INIT_LIST_HEAD(&info->swaplist);
                simple_xattrs_init(&info->xattrs);
                cache_no_acl(inode);
                mapping_set_large_folios(inode->i_mapping);

                switch (mode & S_IFMT) {
                default:
                        inode->i_op = &shmem_special_inode_operations;
                        init_special_inode(inode, mode, dev);
                        break;
                case S_IFREG:
                        inode->i_mapping->a_ops = &shmem_aops;
                        inode->i_op = &shmem_inode_operations;
                        inode->i_fop = &shmem_file_operations;
                        mpol_shared_policy_init(&info->policy,
                                                 shmem_get_sbmpol(sbinfo));
                        break;
                case S_IFDIR:
                        inc_nlink(inode);
                        /* Some things misbehave if size == 0 on a directory */
                        inode->i_size = 2 * BOGO_DIRENT_SIZE;
                        inode->i_op = &shmem_dir_inode_operations;
                        inode->i_fop = &simple_dir_operations;
                        break;
                case S_IFLNK:
                        /*
                         * Must not load anything in the rbtree,
                         * mpol_free_shared_policy will not be called.
                         */
                        mpol_shared_policy_init(&info->policy, NULL);
                        break;
                }

                lockdep_annotate_inode_mutex_key(inode);
        } else
                shmem_free_inode(sb);
        return inode;
}

#ifdef CONFIG_USERFAULTFD
int shmem_mfill_atomic_pte(struct mm_struct *dst_mm,
                           pmd_t *dst_pmd,
                           struct vm_area_struct *dst_vma,
                           unsigned long dst_addr,
                           unsigned long src_addr,
                           bool zeropage, bool wp_copy,
                           struct page **pagep)
{
        struct inode *inode = file_inode(dst_vma->vm_file);
        struct shmem_inode_info *info = SHMEM_I(inode);
        struct address_space *mapping = inode->i_mapping;
        gfp_t gfp = mapping_gfp_mask(mapping);
        pgoff_t pgoff = linear_page_index(dst_vma, dst_addr);
        void *page_kaddr;
        struct folio *folio;
        int ret;
        pgoff_t max_off;

        if (!shmem_inode_acct_block(inode, 1)) {
                /*
                 * We may have got a page, returned -ENOENT triggering a retry,
                 * and now we find ourselves with -ENOMEM. Release the page, to
                 * avoid a BUG_ON in our caller.
                 */
                if (unlikely(*pagep)) {
                        put_page(*pagep);
                        *pagep = NULL;
                }
                return -ENOMEM;
        }

        if (!*pagep) {
                ret = -ENOMEM;
                folio = shmem_alloc_folio(gfp, info, pgoff);
                if (!folio)
                        goto out_unacct_blocks;

                if (!zeropage) {        /* COPY */
                        page_kaddr = kmap_local_folio(folio, 0);
                        /*
                         * The read mmap_lock is held here.  Despite the
                         * mmap_lock being read recursive a deadlock is still
                         * possible if a writer has taken a lock.  For example:
                         *
                         * process A thread 1 takes read lock on own mmap_lock
                         * process A thread 2 calls mmap, blocks taking write lock
                         * process B thread 1 takes page fault, read lock on own mmap lock
                         * process B thread 2 calls mmap, blocks taking write lock
                         * process A thread 1 blocks taking read lock on process B
                         * process B thread 1 blocks taking read lock on process A
                         *
                         * Disable page faults to prevent potential deadlock
                         * and retry the copy outside the mmap_lock.
                         */
                        pagefault_disable();
                        ret = copy_from_user(page_kaddr,
                                             (const void __user *)src_addr,
                                             PAGE_SIZE);
                        pagefault_enable();
                        kunmap_local(page_kaddr);

                        /* fallback to copy_from_user outside mmap_lock */
                        if (unlikely(ret)) {
                                *pagep = &folio->page;
                                ret = -ENOENT;
                                /* don't free the page */
                                goto out_unacct_blocks;
                        }

                        flush_dcache_folio(folio);
                } else {                /* ZEROPAGE */
                        clear_user_highpage(&folio->page, dst_addr);
                }
        } else {
                folio = page_folio(*pagep);
                VM_BUG_ON_FOLIO(folio_test_large(folio), folio);
                *pagep = NULL;
        }

        VM_BUG_ON(folio_test_locked(folio));
        VM_BUG_ON(folio_test_swapbacked(folio));
        __folio_set_locked(folio);
        __folio_set_swapbacked(folio);
        __folio_mark_uptodate(folio);

        ret = -EFAULT;
        max_off = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);
        if (unlikely(pgoff >= max_off))
                goto out_release;

        ret = shmem_add_to_page_cache(folio, mapping, pgoff, NULL,
                                      gfp & GFP_RECLAIM_MASK, dst_mm);
        if (ret)
                goto out_release;

        ret = mfill_atomic_install_pte(dst_mm, dst_pmd, dst_vma, dst_addr,
                                       &folio->page, true, wp_copy);
        if (ret)
                goto out_delete_from_cache;

        spin_lock_irq(&info->lock);
        info->alloced++;
        inode->i_blocks += BLOCKS_PER_PAGE;
        shmem_recalc_inode(inode);
        spin_unlock_irq(&info->lock);

        folio_unlock(folio);
        return 0;
out_delete_from_cache:
        filemap_remove_folio(folio);
out_release:
        folio_unlock(folio);
        folio_put(folio);
out_unacct_blocks:
        shmem_inode_unacct_blocks(inode, 1);
        return ret;
}
#endif /* CONFIG_USERFAULTFD */

#ifdef CONFIG_TMPFS
static const struct inode_operations shmem_symlink_inode_operations;
static const struct inode_operations shmem_short_symlink_operations;

static int
shmem_write_begin(struct file *file, struct address_space *mapping,
                        loff_t pos, unsigned len,
                        struct page **pagep, void **fsdata)
{
        struct inode *inode = mapping->host;
        struct shmem_inode_info *info = SHMEM_I(inode);
        pgoff_t index = pos >> PAGE_SHIFT;
        struct folio *folio;
        int ret = 0;

        /* i_rwsem is held by caller */
        if (unlikely(info->seals & (F_SEAL_GROW |
                                   F_SEAL_WRITE | F_SEAL_FUTURE_WRITE))) {
                if (info->seals & (F_SEAL_WRITE | F_SEAL_FUTURE_WRITE))
                        return -EPERM;
                if ((info->seals & F_SEAL_GROW) && pos + len > inode->i_size)
                        return -EPERM;
        }

        ret = shmem_get_folio(inode, index, &folio, SGP_WRITE);

        if (ret)
                return ret;

        *pagep = folio_file_page(folio, index);
        if (PageHWPoison(*pagep)) {
                folio_unlock(folio);
                folio_put(folio);
                *pagep = NULL;
                return -EIO;
        }

        return 0;
}

static int
shmem_write_end(struct file *file, struct address_space *mapping,
                        loff_t pos, unsigned len, unsigned copied,
                        struct page *page, void *fsdata)
{
        struct inode *inode = mapping->host;

        if (pos + copied > inode->i_size)
                i_size_write(inode, pos + copied);

        if (!PageUptodate(page)) {
                struct page *head = compound_head(page);
                if (PageTransCompound(page)) {
                        int i;

                        for (i = 0; i < HPAGE_PMD_NR; i++) {
                                if (head + i == page)
                                        continue;
                                clear_highpage(head + i);
                                flush_dcache_page(head + i);
                        }
                }
                if (copied < PAGE_SIZE) {
                        unsigned from = pos & (PAGE_SIZE - 1);
                        zero_user_segments(page, 0, from,
                                        from + copied, PAGE_SIZE);
                }
                SetPageUptodate(head);
        }
        set_page_dirty(page);
        unlock_page(page);
        put_page(page);

        return copied;
}

static ssize_t shmem_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
{
        struct file *file = iocb->ki_filp;
        struct inode *inode = file_inode(file);
        struct address_space *mapping = inode->i_mapping;
        pgoff_t index;
        unsigned long offset;
        int error = 0;
        ssize_t retval = 0;
        loff_t *ppos = &iocb->ki_pos;

        index = *ppos >> PAGE_SHIFT;
        offset = *ppos & ~PAGE_MASK;

        for (;;) {
                struct folio *folio = NULL;
                struct page *page = NULL;
                pgoff_t end_index;
                unsigned long nr, ret;
                loff_t i_size = i_size_read(inode);

                end_index = i_size >> PAGE_SHIFT;
                if (index > end_index)
                        break;
                if (index == end_index) {
                        nr = i_size & ~PAGE_MASK;
                        if (nr <= offset)
                                break;
                }

                error = shmem_get_folio(inode, index, &folio, SGP_READ);
                if (error) {
                        if (error == -EINVAL)
                                error = 0;
                        break;
                }
                if (folio) {
                        folio_unlock(folio);

                        page = folio_file_page(folio, index);
                        if (PageHWPoison(page)) {
                                folio_put(folio);
                                error = -EIO;
                                break;
                        }
                }

                /*
                 * We must evaluate after, since reads (unlike writes)
                 * are called without i_rwsem protection against truncate
                 */
                nr = PAGE_SIZE;
                i_size = i_size_read(inode);
                end_index = i_size >> PAGE_SHIFT;
                if (index == end_index) {
                        nr = i_size & ~PAGE_MASK;
                        if (nr <= offset) {
                                if (folio)
                                        folio_put(folio);
                                break;
                        }
                }
                nr -= offset;

                if (folio) {
                        /*
                         * If users can be writing to this page using arbitrary
                         * virtual addresses, take care about potential aliasing
                         * before reading the page on the kernel side.
                         */
                        if (mapping_writably_mapped(mapping))
                                flush_dcache_page(page);
                        /*
                         * Mark the page accessed if we read the beginning.
                         */
                        if (!offset)
                                folio_mark_accessed(folio);
                        /*
                         * Ok, we have the page, and it's up-to-date, so
                         * now we can copy it to user space...
                         */
                        ret = copy_page_to_iter(page, offset, nr, to);
                        folio_put(folio);

                } else if (user_backed_iter(to)) {
                        /*
                         * Copy to user tends to be so well optimized, but
                         * clear_user() not so much, that it is noticeably
                         * faster to copy the zero page instead of clearing.
                         */
                        ret = copy_page_to_iter(ZERO_PAGE(0), offset, nr, to);
                } else {
                        /*
                         * But submitting the same page twice in a row to
                         * splice() - or others? - can result in confusion:
                         * so don't attempt that optimization on pipes etc.
                         */
                        ret = iov_iter_zero(nr, to);
                }

                retval += ret;
                offset += ret;
                index += offset >> PAGE_SHIFT;
                offset &= ~PAGE_MASK;

                if (!iov_iter_count(to))
                        break;
                if (ret < nr) {
                        error = -EFAULT;
                        break;
                }
                cond_resched();
        }

        *ppos = ((loff_t) index << PAGE_SHIFT) + offset;
        file_accessed(file);
        return retval ? retval : error;
}

static loff_t shmem_file_llseek(struct file *file, loff_t offset, int whence)
{
        struct address_space *mapping = file->f_mapping;
        struct inode *inode = mapping->host;

        if (whence != SEEK_DATA && whence != SEEK_HOLE)
                return generic_file_llseek_size(file, offset, whence,
                                        MAX_LFS_FILESIZE, i_size_read(inode));
        if (offset < 0)
                return -ENXIO;

        inode_lock(inode);
        /* We're holding i_rwsem so we can access i_size directly */
        offset = mapping_seek_hole_data(mapping, offset, inode->i_size, whence);
        if (offset >= 0)
                offset = vfs_setpos(file, offset, MAX_LFS_FILESIZE);
        inode_unlock(inode);
        return offset;
}

static long shmem_fallocate(struct file *file, int mode, loff_t offset,
                                                         loff_t len)
{
        struct inode *inode = file_inode(file);
        struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
        struct shmem_inode_info *info = SHMEM_I(inode);
        struct shmem_falloc shmem_falloc;
        pgoff_t start, index, end, undo_fallocend;
        int error;

        if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE))
                return -EOPNOTSUPP;

        inode_lock(inode);

        if (mode & FALLOC_FL_PUNCH_HOLE) {
                struct address_space *mapping = file->f_mapping;
                loff_t unmap_start = round_up(offset, PAGE_SIZE);
                loff_t unmap_end = round_down(offset + len, PAGE_SIZE) - 1;
                DECLARE_WAIT_QUEUE_HEAD_ONSTACK(shmem_falloc_waitq);

                /* protected by i_rwsem */
                if (info->seals & (F_SEAL_WRITE | F_SEAL_FUTURE_WRITE)) {
                        error = -EPERM;
                        goto out;
                }

                shmem_falloc.waitq = &shmem_falloc_waitq;
                shmem_falloc.start = (u64)unmap_start >> PAGE_SHIFT;
                shmem_falloc.next = (unmap_end + 1) >> PAGE_SHIFT;
                spin_lock(&inode->i_lock);
                inode->i_private = &shmem_falloc;
                spin_unlock(&inode->i_lock);

                if ((u64)unmap_end > (u64)unmap_start)
                        unmap_mapping_range(mapping, unmap_start,
                                            1 + unmap_end - unmap_start, 0);
                shmem_truncate_range(inode, offset, offset + len - 1);
                /* No need to unmap again: hole-punching leaves COWed pages */

                spin_lock(&inode->i_lock);
                inode->i_private = NULL;
                wake_up_all(&shmem_falloc_waitq);
                WARN_ON_ONCE(!list_empty(&shmem_falloc_waitq.head));
                spin_unlock(&inode->i_lock);
                error = 0;
                goto out;
        }

        /* We need to check rlimit even when FALLOC_FL_KEEP_SIZE */
        error = inode_newsize_ok(inode, offset + len);
        if (error)
                goto out;

        if ((info->seals & F_SEAL_GROW) && offset + len > inode->i_size) {
                error = -EPERM;
                goto out;
        }

        start = offset >> PAGE_SHIFT;
        end = (offset + len + PAGE_SIZE - 1) >> PAGE_SHIFT;
        /* Try to avoid a swapstorm if len is impossible to satisfy */
        if (sbinfo->max_blocks && end - start > sbinfo->max_blocks) {
                error = -ENOSPC;
                goto out;
        }

        shmem_falloc.waitq = NULL;
        shmem_falloc.start = start;
        shmem_falloc.next  = start;
        shmem_falloc.nr_falloced = 0;
        shmem_falloc.nr_unswapped = 0;
        spin_lock(&inode->i_lock);
        inode->i_private = &shmem_falloc;
        spin_unlock(&inode->i_lock);

        /*
         * info->fallocend is only relevant when huge pages might be
         * involved: to prevent split_huge_page() freeing fallocated
         * pages when FALLOC_FL_KEEP_SIZE committed beyond i_size.
         */
        undo_fallocend = info->fallocend;
        if (info->fallocend < end)
                info->fallocend = end;

        for (index = start; index < end; ) {
                struct folio *folio;

                /*
                 * Good, the fallocate(2) manpage permits EINTR: we may have
                 * been interrupted because we are using up too much memory.
                 */
                if (signal_pending(current))
                        error = -EINTR;
                else if (shmem_falloc.nr_unswapped > shmem_falloc.nr_falloced)
                        error = -ENOMEM;
                else
                        error = shmem_get_folio(inode, index, &folio,
                                                SGP_FALLOC);
                if (error) {
                        info->fallocend = undo_fallocend;
                        /* Remove the !uptodate folios we added */
                        if (index > start) {
                                shmem_undo_range(inode,
                                    (loff_t)start << PAGE_SHIFT,
                                    ((loff_t)index << PAGE_SHIFT) - 1, true);
                        }
                        goto undone;
                }

                /*
                 * Here is a more important optimization than it appears:
                 * a second SGP_FALLOC on the same large folio will clear it,
                 * making it uptodate and un-undoable if we fail later.
                 */
                index = folio_next_index(folio);
                /* Beware 32-bit wraparound */
                if (!index)
                        index--;

                /*
                 * Inform shmem_writepage() how far we have reached.
                 * No need for lock or barrier: we have the page lock.
                 */
                if (!folio_test_uptodate(folio))
                        shmem_falloc.nr_falloced += index - shmem_falloc.next;
                shmem_falloc.next = index;

                /*
                 * If !uptodate, leave it that way so that freeable folios
                 * can be recognized if we need to rollback on error later.
                 * But mark it dirty so that memory pressure will swap rather
                 * than free the folios we are allocating (and SGP_CACHE folios
                 * might still be clean: we now need to mark those dirty too).
                 */
                folio_mark_dirty(folio);
                folio_unlock(folio);
                folio_put(folio);
                cond_resched();
        }

        if (!(mode & FALLOC_FL_KEEP_SIZE) && offset + len > inode->i_size)
                i_size_write(inode, offset + len);
undone:
        spin_lock(&inode->i_lock);
        inode->i_private = NULL;
        spin_unlock(&inode->i_lock);
out:
        if (!error)
                file_modified(file);
        inode_unlock(inode);
        return error;
}

static int shmem_statfs(struct dentry *dentry, struct kstatfs *buf)
{
        struct shmem_sb_info *sbinfo = SHMEM_SB(dentry->d_sb);

        buf->f_type = TMPFS_MAGIC;
        buf->f_bsize = PAGE_SIZE;
        buf->f_namelen = NAME_MAX;
        if (sbinfo->max_blocks) {
                buf->f_blocks = sbinfo->max_blocks;
                buf->f_bavail =
                buf->f_bfree  = sbinfo->max_blocks -
                                percpu_counter_sum(&sbinfo->used_blocks);
        }
        if (sbinfo->max_inodes) {
                buf->f_files = sbinfo->max_inodes;
                buf->f_ffree = sbinfo->free_inodes;
        }
        /* else leave those fields 0 like simple_statfs */

        buf->f_fsid = uuid_to_fsid(dentry->d_sb->s_uuid.b);

        return 0;
}

/*
 * File creation. Allocate an inode, and we're done..
 */
static int
shmem_mknod(struct user_namespace *mnt_userns, struct inode *dir,
            struct dentry *dentry, umode_t mode, dev_t dev)
{
        struct inode *inode;
        int error = -ENOSPC;

        inode = shmem_get_inode(dir->i_sb, dir, mode, dev, VM_NORESERVE);
        if (inode) {
                error = simple_acl_create(dir, inode);
                if (error)
                        goto out_iput;
                error = security_inode_init_security(inode, dir,
                                                     &dentry->d_name,
                                                     shmem_initxattrs, NULL);
                if (error && error != -EOPNOTSUPP)
                        goto out_iput;

                error = 0;
                dir->i_size += BOGO_DIRENT_SIZE;
                dir->i_ctime = dir->i_mtime = current_time(dir);
                inode_inc_iversion(dir);
                d_instantiate(dentry, inode);
                dget(dentry); /* Extra count - pin the dentry in core */
        }
        return error;
out_iput:
        iput(inode);
        return error;
}

static int
shmem_tmpfile(struct user_namespace *mnt_userns, struct inode *dir,
              struct file *file, umode_t mode)
{
        struct inode *inode;
        int error = -ENOSPC;

        inode = shmem_get_inode(dir->i_sb, dir, mode, 0, VM_NORESERVE);
        if (inode) {
                error = security_inode_init_security(inode, dir,
                                                     NULL,
                                                     shmem_initxattrs, NULL);
                if (error && error != -EOPNOTSUPP)
                        goto out_iput;
                error = simple_acl_create(dir, inode);
                if (error)
                        goto out_iput;
                d_tmpfile(file, inode);
        }
        return finish_open_simple(file, error);
out_iput:
        iput(inode);
        return error;
}

static int shmem_mkdir(struct user_namespace *mnt_userns, struct inode *dir,
                       struct dentry *dentry, umode_t mode)
{
        int error;

        if ((error = shmem_mknod(&init_user_ns, dir, dentry,
                                 mode | S_IFDIR, 0)))
                return error;
        inc_nlink(dir);
        return 0;
}

static int shmem_create(struct user_namespace *mnt_userns, struct inode *dir,
                        struct dentry *dentry, umode_t mode, bool excl)
{
        return shmem_mknod(&init_user_ns, dir, dentry, mode | S_IFREG, 0);
}

/*
 * Link a file..
 */
static int shmem_link(struct dentry *old_dentry, struct inode *dir, struct dentry *dentry)
{
        struct inode *inode = d_inode(old_dentry);
        int ret = 0;

        /*
         * No ordinary (disk based) filesystem counts links as inodes;
         * but each new link needs a new dentry, pinning lowmem, and
         * tmpfs dentries cannot be pruned until they are unlinked.
         * But if an O_TMPFILE file is linked into the tmpfs, the
         * first link must skip that, to get the accounting right.
         */
        if (inode->i_nlink) {
                ret = shmem_reserve_inode(inode->i_sb, NULL);
                if (ret)
                        goto out;
        }

        dir->i_size += BOGO_DIRENT_SIZE;
        inode->i_ctime = dir->i_ctime = dir->i_mtime = current_time(inode);
        inode_inc_iversion(dir);
        inc_nlink(inode);
        ihold(inode);   /* New dentry reference */
        dget(dentry);           /* Extra pinning count for the created dentry */
        d_instantiate(dentry, inode);
out:
        return ret;
}

static int shmem_unlink(struct inode *dir, struct dentry *dentry)
{
        struct inode *inode = d_inode(dentry);

        if (inode->i_nlink > 1 && !S_ISDIR(inode->i_mode))
                shmem_free_inode(inode->i_sb);

        dir->i_size -= BOGO_DIRENT_SIZE;
        inode->i_ctime = dir->i_ctime = dir->i_mtime = current_time(inode);
        inode_inc_iversion(dir);
        drop_nlink(inode);
        dput(dentry);   /* Undo the count from "create" - this does all the work */
        return 0;
}

static int shmem_rmdir(struct inode *dir, struct dentry *dentry)
{
        if (!simple_empty(dentry))
                return -ENOTEMPTY;

        drop_nlink(d_inode(dentry));
        drop_nlink(dir);
        return shmem_unlink(dir, dentry);
}

static int shmem_whiteout(struct user_namespace *mnt_userns,
                          struct inode *old_dir, struct dentry *old_dentry)
{
        struct dentry *whiteout;
        int error;

        whiteout = d_alloc(old_dentry->d_parent, &old_dentry->d_name);
        if (!whiteout)
                return -ENOMEM;

        error = shmem_mknod(&init_user_ns, old_dir, whiteout,
                            S_IFCHR | WHITEOUT_MODE, WHITEOUT_DEV);
        dput(whiteout);
        if (error)
                return error;

        /*
         * Cheat and hash the whiteout while the old dentry is still in
         * place, instead of playing games with FS_RENAME_DOES_D_MOVE.
         *
         * d_lookup() will consistently find one of them at this point,
         * not sure which one, but that isn't even important.
         */
        d_rehash(whiteout);
        return 0;
}

/*
 * The VFS layer already does all the dentry stuff for rename,
 * we just have to decrement the usage count for the target if
 * it exists so that the VFS layer correctly free's it when it
 * gets overwritten.
 */
static int shmem_rename2(struct user_namespace *mnt_userns,
                         struct inode *old_dir, struct dentry *old_dentry,
                         struct inode *new_dir, struct dentry *new_dentry,
                         unsigned int flags)
{
        struct inode *inode = d_inode(old_dentry);
        int they_are_dirs = S_ISDIR(inode->i_mode);

        if (flags & ~(RENAME_NOREPLACE | RENAME_EXCHANGE | RENAME_WHITEOUT))
                return -EINVAL;

        if (flags & RENAME_EXCHANGE)
                return simple_rename_exchange(old_dir, old_dentry, new_dir, new_dentry);

        if (!simple_empty(new_dentry))
                return -ENOTEMPTY;

        if (flags & RENAME_WHITEOUT) {
                int error;

                error = shmem_whiteout(&init_user_ns, old_dir, old_dentry);
                if (error)
                        return error;
        }

        if (d_really_is_positive(new_dentry)) {
                (void) shmem_unlink(new_dir, new_dentry);
                if (they_are_dirs) {
                        drop_nlink(d_inode(new_dentry));
                        drop_nlink(old_dir);
                }
        } else if (they_are_dirs) {
                drop_nlink(old_dir);
                inc_nlink(new_dir);
        }

        old_dir->i_size -= BOGO_DIRENT_SIZE;
        new_dir->i_size += BOGO_DIRENT_SIZE;
        old_dir->i_ctime = old_dir->i_mtime =
        new_dir->i_ctime = new_dir->i_mtime =
        inode->i_ctime = current_time(old_dir);
        inode_inc_iversion(old_dir);
        inode_inc_iversion(new_dir);
        return 0;
}

static int shmem_symlink(struct user_namespace *mnt_userns, struct inode *dir,
                         struct dentry *dentry, const char *symname)
{
        int error;
        int len;
        struct inode *inode;
        struct folio *folio;

        len = strlen(symname) + 1;
        if (len > PAGE_SIZE)
                return -ENAMETOOLONG;

        inode = shmem_get_inode(dir->i_sb, dir, S_IFLNK | 0777, 0,
                                VM_NORESERVE);
        if (!inode)
                return -ENOSPC;

        error = security_inode_init_security(inode, dir, &dentry->d_name,
                                             shmem_initxattrs, NULL);
        if (error && error != -EOPNOTSUPP) {
                iput(inode);
                return error;
        }

        inode->i_size = len-1;
        if (len <= SHORT_SYMLINK_LEN) {
                inode->i_link = kmemdup(symname, len, GFP_KERNEL);
                if (!inode->i_link) {
                        iput(inode);
                        return -ENOMEM;
                }
                inode->i_op = &shmem_short_symlink_operations;
        } else {
                inode_nohighmem(inode);
                error = shmem_get_folio(inode, 0, &folio, SGP_WRITE);
                if (error) {
                        iput(inode);
                        return error;
                }
                inode->i_mapping->a_ops = &shmem_aops;
                inode->i_op = &shmem_symlink_inode_operations;
                memcpy(folio_address(folio), symname, len);
                folio_mark_uptodate(folio);
                folio_mark_dirty(folio);
                folio_unlock(folio);
                folio_put(folio);
        }
        dir->i_size += BOGO_DIRENT_SIZE;
        dir->i_ctime = dir->i_mtime = current_time(dir);
        inode_inc_iversion(dir);
        d_instantiate(dentry, inode);
        dget(dentry);
        return 0;
}

static void shmem_put_link(void *arg)
{
        folio_mark_accessed(arg);
        folio_put(arg);
}

static const char *shmem_get_link(struct dentry *dentry,
                                  struct inode *inode,
                                  struct delayed_call *done)
{
        struct folio *folio = NULL;
        int error;

        if (!dentry) {
                folio = filemap_get_folio(inode->i_mapping, 0);
                if (!folio)
                        return ERR_PTR(-ECHILD);
                if (PageHWPoison(folio_page(folio, 0)) ||
                    !folio_test_uptodate(folio)) {
                        folio_put(folio);
                        return ERR_PTR(-ECHILD);
                }
        } else {
                error = shmem_get_folio(inode, 0, &folio, SGP_READ);
                if (error)
                        return ERR_PTR(error);
                if (!folio)
                        return ERR_PTR(-ECHILD);
                if (PageHWPoison(folio_page(folio, 0))) {
                        folio_unlock(folio);
                        folio_put(folio);
                        return ERR_PTR(-ECHILD);
                }
                folio_unlock(folio);
        }
        set_delayed_call(done, shmem_put_link, folio);
        return folio_address(folio);
}

#ifdef CONFIG_TMPFS_XATTR

static int shmem_fileattr_get(struct dentry *dentry, struct fileattr *fa)
{
        struct shmem_inode_info *info = SHMEM_I(d_inode(dentry));

        fileattr_fill_flags(fa, info->fsflags & SHMEM_FL_USER_VISIBLE);

        return 0;
}

static int shmem_fileattr_set(struct user_namespace *mnt_userns,
                              struct dentry *dentry, struct fileattr *fa)
{
        struct inode *inode = d_inode(dentry);
        struct shmem_inode_info *info = SHMEM_I(inode);

        if (fileattr_has_fsx(fa))
                return -EOPNOTSUPP;
        if (fa->flags & ~SHMEM_FL_USER_MODIFIABLE)
                return -EOPNOTSUPP;

        info->fsflags = (info->fsflags & ~SHMEM_FL_USER_MODIFIABLE) |
                (fa->flags & SHMEM_FL_USER_MODIFIABLE);

        shmem_set_inode_flags(inode, info->fsflags);
        inode->i_ctime = current_time(inode);
        inode_inc_iversion(inode);
        return 0;
}

/*
 * Superblocks without xattr inode operations may get some security.* xattr
 * support from the LSM "for free". As soon as we have any other xattrs
 * like ACLs, we also need to implement the security.* handlers at
 * filesystem level, though.
 */

/*
 * Callback for security_inode_init_security() for acquiring xattrs.
 */
static int shmem_initxattrs(struct inode *inode,
                            const struct xattr *xattr_array,
                            void *fs_info)
{
        struct shmem_inode_info *info = SHMEM_I(inode);
        const struct xattr *xattr;
        struct simple_xattr *new_xattr;
        size_t len;

        for (xattr = xattr_array; xattr->name != NULL; xattr++) {
                new_xattr = simple_xattr_alloc(xattr->value, xattr->value_len);
                if (!new_xattr)
                        return -ENOMEM;

                len = strlen(xattr->name) + 1;
                new_xattr->name = kmalloc(XATTR_SECURITY_PREFIX_LEN + len,
                                          GFP_KERNEL);
                if (!new_xattr->name) {
                        kvfree(new_xattr);
                        return -ENOMEM;
                }

                memcpy(new_xattr->name, XATTR_SECURITY_PREFIX,
                       XATTR_SECURITY_PREFIX_LEN);
                memcpy(new_xattr->name + XATTR_SECURITY_PREFIX_LEN,
                       xattr->name, len);

                simple_xattr_list_add(&info->xattrs, new_xattr);
        }

        return 0;
}

static int shmem_xattr_handler_get(const struct xattr_handler *handler,
                                   struct dentry *unused, struct inode *inode,
                                   const char *name, void *buffer, size_t size)
{
        struct shmem_inode_info *info = SHMEM_I(inode);

        name = xattr_full_name(handler, name);
        return simple_xattr_get(&info->xattrs, name, buffer, size);
}

static int shmem_xattr_handler_set(const struct xattr_handler *handler,
                                   struct user_namespace *mnt_userns,
                                   struct dentry *unused, struct inode *inode,
                                   const char *name, const void *value,
                                   size_t size, int flags)
{
        struct shmem_inode_info *info = SHMEM_I(inode);
        int err;

        name = xattr_full_name(handler, name);
        err = simple_xattr_set(&info->xattrs, name, value, size, flags, NULL);
        if (!err) {
                inode->i_ctime = current_time(inode);
                inode_inc_iversion(inode);
        }
        return err;
}

static const struct xattr_handler shmem_security_xattr_handler = {
        .prefix = XATTR_SECURITY_PREFIX,
        .get = shmem_xattr_handler_get,
        .set = shmem_xattr_handler_set,
};

static const struct xattr_handler shmem_trusted_xattr_handler = {
        .prefix = XATTR_TRUSTED_PREFIX,
        .get = shmem_xattr_handler_get,
        .set = shmem_xattr_handler_set,
};

static const struct xattr_handler *shmem_xattr_handlers[] = {
#ifdef CONFIG_TMPFS_POSIX_ACL
        &posix_acl_access_xattr_handler,
        &posix_acl_default_xattr_handler,
#endif
        &shmem_security_xattr_handler,
        &shmem_trusted_xattr_handler,
        NULL
};

static ssize_t shmem_listxattr(struct dentry *dentry, char *buffer, size_t size)
{
        struct shmem_inode_info *info = SHMEM_I(d_inode(dentry));
        return simple_xattr_list(d_inode(dentry), &info->xattrs, buffer, size);
}
#endif /* CONFIG_TMPFS_XATTR */

static const struct inode_operations shmem_short_symlink_operations = {
        .getattr        = shmem_getattr,
        .get_link       = simple_get_link,
#ifdef CONFIG_TMPFS_XATTR
        .listxattr      = shmem_listxattr,
#endif
};

static const struct inode_operations shmem_symlink_inode_operations = {
        .getattr        = shmem_getattr,
        .get_link       = shmem_get_link,
#ifdef CONFIG_TMPFS_XATTR
        .listxattr      = shmem_listxattr,
#endif
};

static struct dentry *shmem_get_parent(struct dentry *child)
{
        return ERR_PTR(-ESTALE);
}

static int shmem_match(struct inode *ino, void *vfh)
{
        __u32 *fh = vfh;
        __u64 inum = fh[2];
        inum = (inum << 32) | fh[1];
        return ino->i_ino == inum && fh[0] == ino->i_generation;
}

/* Find any alias of inode, but prefer a hashed alias */
static struct dentry *shmem_find_alias(struct inode *inode)
{
        struct dentry *alias = d_find_alias(inode);

        return alias ?: d_find_any_alias(inode);
}


static struct dentry *shmem_fh_to_dentry(struct super_block *sb,
                struct fid *fid, int fh_len, int fh_type)
{
        struct inode *inode;
        struct dentry *dentry = NULL;
        u64 inum;

        if (fh_len < 3)
                return NULL;

        inum = fid->raw[2];
        inum = (inum << 32) | fid->raw[1];

        inode = ilookup5(sb, (unsigned long)(inum + fid->raw[0]),
                        shmem_match, fid->raw);
        if (inode) {
                dentry = shmem_find_alias(inode);
                iput(inode);
        }

        return dentry;
}

static int shmem_encode_fh(struct inode *inode, __u32 *fh, int *len,
                                struct inode *parent)
{
        if (*len < 3) {
                *len = 3;
                return FILEID_INVALID;
        }

        if (inode_unhashed(inode)) {
                /* Unfortunately insert_inode_hash is not idempotent,
                 * so as we hash inodes here rather than at creation
                 * time, we need a lock to ensure we only try
                 * to do it once
                 */
                static DEFINE_SPINLOCK(lock);
                spin_lock(&lock);
                if (inode_unhashed(inode))
                        __insert_inode_hash(inode,
                                            inode->i_ino + inode->i_generation);
                spin_unlock(&lock);
        }

        fh[0] = inode->i_generation;
        fh[1] = inode->i_ino;
        fh[2] = ((__u64)inode->i_ino) >> 32;

        *len = 3;
        return 1;
}

static const struct export_operations shmem_export_ops = {
        .get_parent     = shmem_get_parent,
        .encode_fh      = shmem_encode_fh,
        .fh_to_dentry   = shmem_fh_to_dentry,
};

enum shmem_param {
        Opt_gid,
        Opt_huge,
        Opt_mode,
        Opt_mpol,
        Opt_nr_blocks,
        Opt_nr_inodes,
        Opt_size,
        Opt_uid,
        Opt_inode32,
        Opt_inode64,
};

static const struct constant_table shmem_param_enums_huge[] = {
        {"never",       SHMEM_HUGE_NEVER },
        {"always",      SHMEM_HUGE_ALWAYS },
        {"within_size", SHMEM_HUGE_WITHIN_SIZE },
        {"advise",      SHMEM_HUGE_ADVISE },
        {}
};

const struct fs_parameter_spec shmem_fs_parameters[] = {
        fsparam_u32   ("gid",           Opt_gid),
        fsparam_enum  ("huge",          Opt_huge,  shmem_param_enums_huge),
        fsparam_u32oct("mode",          Opt_mode),
        fsparam_string("mpol",          Opt_mpol),
        fsparam_string("nr_blocks",     Opt_nr_blocks),
        fsparam_string("nr_inodes",     Opt_nr_inodes),
        fsparam_string("size",          Opt_size),
        fsparam_u32   ("uid",           Opt_uid),
        fsparam_flag  ("inode32",       Opt_inode32),
        fsparam_flag  ("inode64",       Opt_inode64),
        {}
};

static int shmem_parse_one(struct fs_context *fc, struct fs_parameter *param)
{
        struct shmem_options *ctx = fc->fs_private;
        struct fs_parse_result result;
        unsigned long long size;
        char *rest;
        int opt;

        opt = fs_parse(fc, shmem_fs_parameters, param, &result);
        if (opt < 0)
                return opt;

        switch (opt) {
        case Opt_size:
                size = memparse(param->string, &rest);
                if (*rest == '%') {
                        size <<= PAGE_SHIFT;
                        size *= totalram_pages();
                        do_div(size, 100);
                        rest++;
                }
                if (*rest)
                        goto bad_value;
                ctx->blocks = DIV_ROUND_UP(size, PAGE_SIZE);
                ctx->seen |= SHMEM_SEEN_BLOCKS;
                break;
        case Opt_nr_blocks:
                ctx->blocks = memparse(param->string, &rest);
                if (*rest || ctx->blocks > S64_MAX)
                        goto bad_value;
                ctx->seen |= SHMEM_SEEN_BLOCKS;
                break;
        case Opt_nr_inodes:
                ctx->inodes = memparse(param->string, &rest);
                if (*rest)
                        goto bad_value;
                ctx->seen |= SHMEM_SEEN_INODES;
                break;
        case Opt_mode:
                ctx->mode = result.uint_32 & 07777;
                break;
        case Opt_uid:
                ctx->uid = make_kuid(current_user_ns(), result.uint_32);
                if (!uid_valid(ctx->uid))
                        goto bad_value;
                break;
        case Opt_gid:
                ctx->gid = make_kgid(current_user_ns(), result.uint_32);
                if (!gid_valid(ctx->gid))
                        goto bad_value;
                break;
        case Opt_huge:
                ctx->huge = result.uint_32;
                if (ctx->huge != SHMEM_HUGE_NEVER &&
                    !(IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) &&
                      has_transparent_hugepage()))
                        goto unsupported_parameter;
                ctx->seen |= SHMEM_SEEN_HUGE;
                break;
        case Opt_mpol:
                if (IS_ENABLED(CONFIG_NUMA)) {
                        mpol_put(ctx->mpol);
                        ctx->mpol = NULL;
                        if (mpol_parse_str(param->string, &ctx->mpol))
                                goto bad_value;
                        break;
                }
                goto unsupported_parameter;
        case Opt_inode32:
                ctx->full_inums = false;
                ctx->seen |= SHMEM_SEEN_INUMS;
                break;
        case Opt_inode64:
                if (sizeof(ino_t) < 8) {
                        return invalfc(fc,
                                       "Cannot use inode64 with <64bit inums in kernel\n");
                }
                ctx->full_inums = true;
                ctx->seen |= SHMEM_SEEN_INUMS;
                break;
        }
        return 0;

unsupported_parameter:
        return invalfc(fc, "Unsupported parameter '%s'", param->key);
bad_value:
        return invalfc(fc, "Bad value for '%s'", param->key);
}

static int shmem_parse_options(struct fs_context *fc, void *data)
{
        char *options = data;

        if (options) {
                int err = security_sb_eat_lsm_opts(options, &fc->security);
                if (err)
                        return err;
        }

        while (options != NULL) {
                char *this_char = options;
                for (;;) {
                        /*
                         * NUL-terminate this option: unfortunately,
                         * mount options form a comma-separated list,
                         * but mpol's nodelist may also contain commas.
                         */
                        options = strchr(options, ',');
                        if (options == NULL)
                                break;
                        options++;
                        if (!isdigit(*options)) {
                                options[-1] = '\0';
                                break;
                        }
                }
                if (*this_char) {
                        char *value = strchr(this_char, '=');
                        size_t len = 0;
                        int err;

                        if (value) {
                                *value++ = '\0';
                                len = strlen(value);
                        }
                        err = vfs_parse_fs_string(fc, this_char, value, len);
                        if (err < 0)
                                return err;
                }
        }
        return 0;
}

/*
 * Reconfigure a shmem filesystem.
 *
 * Note that we disallow change from limited->unlimited blocks/inodes while any
 * are in use; but we must separately disallow unlimited->limited, because in
 * that case we have no record of how much is already in use.
 */
static int shmem_reconfigure(struct fs_context *fc)
{
        struct shmem_options *ctx = fc->fs_private;
        struct shmem_sb_info *sbinfo = SHMEM_SB(fc->root->d_sb);
        unsigned long inodes;
        struct mempolicy *mpol = NULL;
        const char *err;

        raw_spin_lock(&sbinfo->stat_lock);
        inodes = sbinfo->max_inodes - sbinfo->free_inodes;

        if ((ctx->seen & SHMEM_SEEN_BLOCKS) && ctx->blocks) {
                if (!sbinfo->max_blocks) {
                        err = "Cannot retroactively limit size";
                        goto out;
                }
                if (percpu_counter_compare(&sbinfo->used_blocks,
                                           ctx->blocks) > 0) {
                        err = "Too small a size for current use";
                        goto out;
                }
        }
        if ((ctx->seen & SHMEM_SEEN_INODES) && ctx->inodes) {
                if (!sbinfo->max_inodes) {
                        err = "Cannot retroactively limit inodes";
                        goto out;
                }
                if (ctx->inodes < inodes) {
                        err = "Too few inodes for current use";
                        goto out;
                }
        }

        if ((ctx->seen & SHMEM_SEEN_INUMS) && !ctx->full_inums &&
            sbinfo->next_ino > UINT_MAX) {
                err = "Current inum too high to switch to 32-bit inums";
                goto out;
        }

        if (ctx->seen & SHMEM_SEEN_HUGE)
                sbinfo->huge = ctx->huge;
        if (ctx->seen & SHMEM_SEEN_INUMS)
                sbinfo->full_inums = ctx->full_inums;
        if (ctx->seen & SHMEM_SEEN_BLOCKS)
                sbinfo->max_blocks  = ctx->blocks;
        if (ctx->seen & SHMEM_SEEN_INODES) {
                sbinfo->max_inodes  = ctx->inodes;
                sbinfo->free_inodes = ctx->inodes - inodes;
        }

        /*
         * Preserve previous mempolicy unless mpol remount option was specified.
         */
        if (ctx->mpol) {
                mpol = sbinfo->mpol;
                sbinfo->mpol = ctx->mpol;       /* transfers initial ref */
                ctx->mpol = NULL;
        }
        raw_spin_unlock(&sbinfo->stat_lock);
        mpol_put(mpol);
        return 0;
out:
        raw_spin_unlock(&sbinfo->stat_lock);
        return invalfc(fc, "%s", err);
}

static int shmem_show_options(struct seq_file *seq, struct dentry *root)
{
        struct shmem_sb_info *sbinfo = SHMEM_SB(root->d_sb);

        if (sbinfo->max_blocks != shmem_default_max_blocks())
                seq_printf(seq, ",size=%luk",
                        sbinfo->max_blocks << (PAGE_SHIFT - 10));
        if (sbinfo->max_inodes != shmem_default_max_inodes())
                seq_printf(seq, ",nr_inodes=%lu", sbinfo->max_inodes);
        if (sbinfo->mode != (0777 | S_ISVTX))
                seq_printf(seq, ",mode=%03ho", sbinfo->mode);
        if (!uid_eq(sbinfo->uid, GLOBAL_ROOT_UID))
                seq_printf(seq, ",uid=%u",
                                from_kuid_munged(&init_user_ns, sbinfo->uid));
        if (!gid_eq(sbinfo->gid, GLOBAL_ROOT_GID))
                seq_printf(seq, ",gid=%u",
                                from_kgid_munged(&init_user_ns, sbinfo->gid));

        /*
         * Showing inode{64,32} might be useful even if it's the system default,
         * since then people don't have to resort to checking both here and
         * /proc/config.gz to confirm 64-bit inums were successfully applied
         * (which may not even exist if IKCONFIG_PROC isn't enabled).
         *
         * We hide it when inode64 isn't the default and we are using 32-bit
         * inodes, since that probably just means the feature isn't even under
         * consideration.
         *
         * As such:
         *
         *                     +-----------------+-----------------+
         *                     | TMPFS_INODE64=y | TMPFS_INODE64=n |
         *  +------------------+-----------------+-----------------+
         *  | full_inums=true  | show            | show            |
         *  | full_inums=false | show            | hide            |
         *  +------------------+-----------------+-----------------+
         *
         */
        if (IS_ENABLED(CONFIG_TMPFS_INODE64) || sbinfo->full_inums)
                seq_printf(seq, ",inode%d", (sbinfo->full_inums ? 64 : 32));
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
        /* Rightly or wrongly, show huge mount option unmasked by shmem_huge */
        if (sbinfo->huge)
                seq_printf(seq, ",huge=%s", shmem_format_huge(sbinfo->huge));
#endif
        shmem_show_mpol(seq, sbinfo->mpol);
        return 0;
}

#endif /* CONFIG_TMPFS */

static void shmem_put_super(struct super_block *sb)
{
        struct shmem_sb_info *sbinfo = SHMEM_SB(sb);

        free_percpu(sbinfo->ino_batch);
        percpu_counter_destroy(&sbinfo->used_blocks);
        mpol_put(sbinfo->mpol);
        kfree(sbinfo);
        sb->s_fs_info = NULL;
}

static int shmem_fill_super(struct super_block *sb, struct fs_context *fc)
{
        struct shmem_options *ctx = fc->fs_private;
        struct inode *inode;
        struct shmem_sb_info *sbinfo;

        /* Round up to L1_CACHE_BYTES to resist false sharing */
        sbinfo = kzalloc(max((int)sizeof(struct shmem_sb_info),
                                L1_CACHE_BYTES), GFP_KERNEL);
        if (!sbinfo)
                return -ENOMEM;

        sb->s_fs_info = sbinfo;

#ifdef CONFIG_TMPFS
        /*
         * Per default we only allow half of the physical ram per
         * tmpfs instance, limiting inodes to one per page of lowmem;
         * but the internal instance is left unlimited.
         */
        if (!(sb->s_flags & SB_KERNMOUNT)) {
                if (!(ctx->seen & SHMEM_SEEN_BLOCKS))
                        ctx->blocks = shmem_default_max_blocks();
                if (!(ctx->seen & SHMEM_SEEN_INODES))
                        ctx->inodes = shmem_default_max_inodes();
                if (!(ctx->seen & SHMEM_SEEN_INUMS))
                        ctx->full_inums = IS_ENABLED(CONFIG_TMPFS_INODE64);
        } else {
                sb->s_flags |= SB_NOUSER;
        }
        sb->s_export_op = &shmem_export_ops;
        sb->s_flags |= SB_NOSEC | SB_I_VERSION;
#else
        sb->s_flags |= SB_NOUSER;
#endif
        sbinfo->max_blocks = ctx->blocks;
        sbinfo->free_inodes = sbinfo->max_inodes = ctx->inodes;
        if (sb->s_flags & SB_KERNMOUNT) {
                sbinfo->ino_batch = alloc_percpu(ino_t);
                if (!sbinfo->ino_batch)
                        goto failed;
        }
        sbinfo->uid = ctx->uid;
        sbinfo->gid = ctx->gid;
        sbinfo->full_inums = ctx->full_inums;
        sbinfo->mode = ctx->mode;
        sbinfo->huge = ctx->huge;
        sbinfo->mpol = ctx->mpol;
        ctx->mpol = NULL;

        raw_spin_lock_init(&sbinfo->stat_lock);
        if (percpu_counter_init(&sbinfo->used_blocks, 0, GFP_KERNEL))
                goto failed;
        spin_lock_init(&sbinfo->shrinklist_lock);
        INIT_LIST_HEAD(&sbinfo->shrinklist);

        sb->s_maxbytes = MAX_LFS_FILESIZE;
        sb->s_blocksize = PAGE_SIZE;
        sb->s_blocksize_bits = PAGE_SHIFT;
        sb->s_magic = TMPFS_MAGIC;
        sb->s_op = &shmem_ops;
        sb->s_time_gran = 1;
#ifdef CONFIG_TMPFS_XATTR
        sb->s_xattr = shmem_xattr_handlers;
#endif
#ifdef CONFIG_TMPFS_POSIX_ACL
        sb->s_flags |= SB_POSIXACL;
#endif
        uuid_gen(&sb->s_uuid);

        inode = shmem_get_inode(sb, NULL, S_IFDIR | sbinfo->mode, 0, VM_NORESERVE);
        if (!inode)
                goto failed;
        inode->i_uid = sbinfo->uid;
        inode->i_gid = sbinfo->gid;
        sb->s_root = d_make_root(inode);
        if (!sb->s_root)
                goto failed;
        return 0;

failed:
        shmem_put_super(sb);
        return -ENOMEM;
}

static int shmem_get_tree(struct fs_context *fc)
{
        return get_tree_nodev(fc, shmem_fill_super);
}

static void shmem_free_fc(struct fs_context *fc)
{
        struct shmem_options *ctx = fc->fs_private;

        if (ctx) {
                mpol_put(ctx->mpol);
                kfree(ctx);
        }
}

static const struct fs_context_operations shmem_fs_context_ops = {
        .free                   = shmem_free_fc,
        .get_tree               = shmem_get_tree,
#ifdef CONFIG_TMPFS
        .parse_monolithic       = shmem_parse_options,
        .parse_param            = shmem_parse_one,
        .reconfigure            = shmem_reconfigure,
#endif
};

static struct kmem_cache *shmem_inode_cachep;

static struct inode *shmem_alloc_inode(struct super_block *sb)
{
        struct shmem_inode_info *info;
        info = alloc_inode_sb(sb, shmem_inode_cachep, GFP_KERNEL);
        if (!info)
                return NULL;
        return &info->vfs_inode;
}

static void shmem_free_in_core_inode(struct inode *inode)
{
        if (S_ISLNK(inode->i_mode))
                kfree(inode->i_link);
        kmem_cache_free(shmem_inode_cachep, SHMEM_I(inode));
}

static void shmem_destroy_inode(struct inode *inode)
{
        if (S_ISREG(inode->i_mode))
                mpol_free_shared_policy(&SHMEM_I(inode)->policy);
}

static void shmem_init_inode(void *foo)
{
        struct shmem_inode_info *info = foo;
        inode_init_once(&info->vfs_inode);
}

static void shmem_init_inodecache(void)
{
        shmem_inode_cachep = kmem_cache_create("shmem_inode_cache",
                                sizeof(struct shmem_inode_info),
                                0, SLAB_PANIC|SLAB_ACCOUNT, shmem_init_inode);
}

static void shmem_destroy_inodecache(void)
{
        kmem_cache_destroy(shmem_inode_cachep);
}

/* Keep the page in page cache instead of truncating it */
static int shmem_error_remove_page(struct address_space *mapping,
                                   struct page *page)
{
        return 0;
}

const struct address_space_operations shmem_aops = {
        .writepage      = shmem_writepage,
        .dirty_folio    = noop_dirty_folio,
#ifdef CONFIG_TMPFS
        .write_begin    = shmem_write_begin,
        .write_end      = shmem_write_end,
#endif
#ifdef CONFIG_MIGRATION
        .migrate_folio  = migrate_folio,
#endif
        .error_remove_page = shmem_error_remove_page,
};
EXPORT_SYMBOL(shmem_aops);

static const struct file_operations shmem_file_operations = {
        .mmap           = shmem_mmap,
        .open           = generic_file_open,
        .get_unmapped_area = shmem_get_unmapped_area,
#ifdef CONFIG_TMPFS
        .llseek         = shmem_file_llseek,
        .read_iter      = shmem_file_read_iter,
        .write_iter     = generic_file_write_iter,
        .fsync          = noop_fsync,
        .splice_read    = generic_file_splice_read,
        .splice_write   = iter_file_splice_write,
        .fallocate      = shmem_fallocate,
#endif
};

static const struct inode_operations shmem_inode_operations = {
        .getattr        = shmem_getattr,
        .setattr        = shmem_setattr,
#ifdef CONFIG_TMPFS_XATTR
        .listxattr      = shmem_listxattr,
        .set_acl        = simple_set_acl,
        .fileattr_get   = shmem_fileattr_get,
        .fileattr_set   = shmem_fileattr_set,
#endif
};

static const struct inode_operations shmem_dir_inode_operations = {
#ifdef CONFIG_TMPFS
        .getattr        = shmem_getattr,
        .create         = shmem_create,
        .lookup         = simple_lookup,
        .link           = shmem_link,
        .unlink         = shmem_unlink,
        .symlink        = shmem_symlink,
        .mkdir          = shmem_mkdir,
        .rmdir          = shmem_rmdir,
        .mknod          = shmem_mknod,
        .rename         = shmem_rename2,
        .tmpfile        = shmem_tmpfile,
#endif
#ifdef CONFIG_TMPFS_XATTR
        .listxattr      = shmem_listxattr,
        .fileattr_get   = shmem_fileattr_get,
        .fileattr_set   = shmem_fileattr_set,
#endif
#ifdef CONFIG_TMPFS_POSIX_ACL
        .setattr        = shmem_setattr,
        .set_acl        = simple_set_acl,
#endif
};

static const struct inode_operations shmem_special_inode_operations = {
        .getattr        = shmem_getattr,
#ifdef CONFIG_TMPFS_XATTR
        .listxattr      = shmem_listxattr,
#endif
#ifdef CONFIG_TMPFS_POSIX_ACL
        .setattr        = shmem_setattr,
        .set_acl        = simple_set_acl,
#endif
};

static const struct super_operations shmem_ops = {
        .alloc_inode    = shmem_alloc_inode,
        .free_inode     = shmem_free_in_core_inode,
        .destroy_inode  = shmem_destroy_inode,
#ifdef CONFIG_TMPFS
        .statfs         = shmem_statfs,
        .show_options   = shmem_show_options,
#endif
        .evict_inode    = shmem_evict_inode,
        .drop_inode     = generic_delete_inode,
        .put_super      = shmem_put_super,
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
        .nr_cached_objects      = shmem_unused_huge_count,
        .free_cached_objects    = shmem_unused_huge_scan,
#endif
};

static const struct vm_operations_struct shmem_vm_ops = {
        .fault          = shmem_fault,
        .map_pages      = filemap_map_pages,
#ifdef CONFIG_NUMA
        .set_policy     = shmem_set_policy,
        .get_policy     = shmem_get_policy,
#endif
};

int shmem_init_fs_context(struct fs_context *fc)
{
        struct shmem_options *ctx;

        ctx = kzalloc(sizeof(struct shmem_options), GFP_KERNEL);
        if (!ctx)
                return -ENOMEM;

        ctx->mode = 0777 | S_ISVTX;
        ctx->uid = current_fsuid();
        ctx->gid = current_fsgid();

        fc->fs_private = ctx;
        fc->ops = &shmem_fs_context_ops;
        return 0;
}

static struct file_system_type shmem_fs_type = {
        .owner          = THIS_MODULE,
        .name           = "tmpfs",
        .init_fs_context = shmem_init_fs_context,
#ifdef CONFIG_TMPFS
        .parameters     = shmem_fs_parameters,
#endif
        .kill_sb        = kill_litter_super,
        .fs_flags       = FS_USERNS_MOUNT,
};

void __init shmem_init(void)
{
        int error;

        shmem_init_inodecache();

        error = register_filesystem(&shmem_fs_type);
        if (error) {
                pr_err("Could not register tmpfs\n");
                goto out2;
        }

        shm_mnt = kern_mount(&shmem_fs_type);
        if (IS_ERR(shm_mnt)) {
                error = PTR_ERR(shm_mnt);
                pr_err("Could not kern_mount tmpfs\n");
                goto out1;
        }

#ifdef CONFIG_TRANSPARENT_HUGEPAGE
        if (has_transparent_hugepage() && shmem_huge > SHMEM_HUGE_DENY)
                SHMEM_SB(shm_mnt->mnt_sb)->huge = shmem_huge;
        else
                shmem_huge = SHMEM_HUGE_NEVER; /* just in case it was patched */
#endif
        return;

out1:
        unregister_filesystem(&shmem_fs_type);
out2:
        shmem_destroy_inodecache();
        shm_mnt = ERR_PTR(error);
}

#if defined(CONFIG_TRANSPARENT_HUGEPAGE) && defined(CONFIG_SYSFS)
static ssize_t shmem_enabled_show(struct kobject *kobj,
                                  struct kobj_attribute *attr, char *buf)
{
        static const int values[] = {
                SHMEM_HUGE_ALWAYS,
                SHMEM_HUGE_WITHIN_SIZE,
                SHMEM_HUGE_ADVISE,
                SHMEM_HUGE_NEVER,
                SHMEM_HUGE_DENY,
                SHMEM_HUGE_FORCE,
        };
        int len = 0;
        int i;

        for (i = 0; i < ARRAY_SIZE(values); i++) {
                len += sysfs_emit_at(buf, len,
                                     shmem_huge == values[i] ? "%s[%s]" : "%s%s",
                                     i ? " " : "",
                                     shmem_format_huge(values[i]));
        }

        len += sysfs_emit_at(buf, len, "\n");

        return len;
}

static ssize_t shmem_enabled_store(struct kobject *kobj,
                struct kobj_attribute *attr, const char *buf, size_t count)
{
        char tmp[16];
        int huge;

        if (count + 1 > sizeof(tmp))
                return -EINVAL;
        memcpy(tmp, buf, count);
        tmp[count] = '\0';
        if (count && tmp[count - 1] == '\n')
                tmp[count - 1] = '\0';

        huge = shmem_parse_huge(tmp);
        if (huge == -EINVAL)
                return -EINVAL;
        if (!has_transparent_hugepage() &&
                        huge != SHMEM_HUGE_NEVER && huge != SHMEM_HUGE_DENY)
                return -EINVAL;

        shmem_huge = huge;
        if (shmem_huge > SHMEM_HUGE_DENY)
                SHMEM_SB(shm_mnt->mnt_sb)->huge = shmem_huge;
        return count;
}

struct kobj_attribute shmem_enabled_attr = __ATTR_RW(shmem_enabled);
#endif /* CONFIG_TRANSPARENT_HUGEPAGE && CONFIG_SYSFS */

#else /* !CONFIG_SHMEM */

/*
 * tiny-shmem: simple shmemfs and tmpfs using ramfs code
 *
 * This is intended for small system where the benefits of the full
 * shmem code (swap-backed and resource-limited) are outweighed by
 * their complexity. On systems without swap this code should be
 * effectively equivalent, but much lighter weight.
 */

static struct file_system_type shmem_fs_type = {
        .name           = "tmpfs",
        .init_fs_context = ramfs_init_fs_context,
        .parameters     = ramfs_fs_parameters,
        .kill_sb        = kill_litter_super,
        .fs_flags       = FS_USERNS_MOUNT,
};

void __init shmem_init(void)
{
        BUG_ON(register_filesystem(&shmem_fs_type) != 0);

        shm_mnt = kern_mount(&shmem_fs_type);
        BUG_ON(IS_ERR(shm_mnt));
}

int shmem_unuse(unsigned int type)
{
        return 0;
}

int shmem_lock(struct file *file, int lock, struct ucounts *ucounts)
{
        return 0;
}

void shmem_unlock_mapping(struct address_space *mapping)
{
}

#ifdef CONFIG_MMU
unsigned long shmem_get_unmapped_area(struct file *file,
                                      unsigned long addr, unsigned long len,
                                      unsigned long pgoff, unsigned long flags)
{
        return current->mm->get_unmapped_area(file, addr, len, pgoff, flags);
}
#endif

void shmem_truncate_range(struct inode *inode, loff_t lstart, loff_t lend)
{
        truncate_inode_pages_range(inode->i_mapping, lstart, lend);
}
EXPORT_SYMBOL_GPL(shmem_truncate_range);

#define shmem_vm_ops                            generic_file_vm_ops
#define shmem_file_operations                   ramfs_file_operations
#define shmem_get_inode(sb, dir, mode, dev, flags)      ramfs_get_inode(sb, dir, mode, dev)
#define shmem_acct_size(flags, size)            0
#define shmem_unacct_size(flags, size)          do {} while (0)

#endif /* CONFIG_SHMEM */

/* common code */

static struct file *__shmem_file_setup(struct vfsmount *mnt, const char *name, loff_t size,
                                       unsigned long flags, unsigned int i_flags)
{
        struct inode *inode;
        struct file *res;

        if (IS_ERR(mnt))
                return ERR_CAST(mnt);

        if (size < 0 || size > MAX_LFS_FILESIZE)
                return ERR_PTR(-EINVAL);

        if (shmem_acct_size(flags, size))
                return ERR_PTR(-ENOMEM);

        inode = shmem_get_inode(mnt->mnt_sb, NULL, S_IFREG | S_IRWXUGO, 0,
                                flags);
        if (unlikely(!inode)) {
                shmem_unacct_size(flags, size);
                return ERR_PTR(-ENOSPC);
        }
        inode->i_flags |= i_flags;
        inode->i_size = size;
        clear_nlink(inode);     /* It is unlinked */
        res = ERR_PTR(ramfs_nommu_expand_for_mapping(inode, size));
        if (!IS_ERR(res))
                res = alloc_file_pseudo(inode, mnt, name, O_RDWR,
                                &shmem_file_operations);
        if (IS_ERR(res))
                iput(inode);
        return res;
}

/**
 * shmem_kernel_file_setup - get an unlinked file living in tmpfs which must be
 *      kernel internal.  There will be NO LSM permission checks against the
 *      underlying inode.  So users of this interface must do LSM checks at a
 *      higher layer.  The users are the big_key and shm implementations.  LSM
 *      checks are provided at the key or shm level rather than the inode.
 * @name: name for dentry (to be seen in /proc/<pid>/maps
 * @size: size to be set for the file
 * @flags: VM_NORESERVE suppresses pre-accounting of the entire object size
 */
struct file *shmem_kernel_file_setup(const char *name, loff_t size, unsigned long flags)
{
        return __shmem_file_setup(shm_mnt, name, size, flags, S_PRIVATE);
}

/**
 * shmem_file_setup - get an unlinked file living in tmpfs
 * @name: name for dentry (to be seen in /proc/<pid>/maps
 * @size: size to be set for the file
 * @flags: VM_NORESERVE suppresses pre-accounting of the entire object size
 */
struct file *shmem_file_setup(const char *name, loff_t size, unsigned long flags)
{
        return __shmem_file_setup(shm_mnt, name, size, flags, 0);
}
EXPORT_SYMBOL_GPL(shmem_file_setup);

/**
 * shmem_file_setup_with_mnt - get an unlinked file living in tmpfs
 * @mnt: the tmpfs mount where the file will be created
 * @name: name for dentry (to be seen in /proc/<pid>/maps
 * @size: size to be set for the file
 * @flags: VM_NORESERVE suppresses pre-accounting of the entire object size
 */
struct file *shmem_file_setup_with_mnt(struct vfsmount *mnt, const char *name,
                                       loff_t size, unsigned long flags)
{
        return __shmem_file_setup(mnt, name, size, flags, 0);
}
EXPORT_SYMBOL_GPL(shmem_file_setup_with_mnt);

/**
 * shmem_zero_setup - setup a shared anonymous mapping
 * @vma: the vma to be mmapped is prepared by do_mmap
 */
int shmem_zero_setup(struct vm_area_struct *vma)
{
        struct file *file;
        loff_t size = vma->vm_end - vma->vm_start;

        /*
         * Cloning a new file under mmap_lock leads to a lock ordering conflict
         * between XFS directory reading and selinux: since this file is only
         * accessible to the user through its mapping, use S_PRIVATE flag to
         * bypass file security, in the same way as shmem_kernel_file_setup().
         */
        file = shmem_kernel_file_setup("dev/zero", size, vma->vm_flags);
        if (IS_ERR(file))
                return PTR_ERR(file);

        if (vma->vm_file)
                fput(vma->vm_file);
        vma->vm_file = file;
        vma->vm_ops = &shmem_vm_ops;

        return 0;
}

/**
 * shmem_read_mapping_page_gfp - read into page cache, using specified page allocation flags.
 * @mapping:    the page's address_space
 * @index:      the page index
 * @gfp:        the page allocator flags to use if allocating
 *
 * This behaves as a tmpfs "read_cache_page_gfp(mapping, index, gfp)",
 * with any new page allocations done using the specified allocation flags.
 * But read_cache_page_gfp() uses the ->read_folio() method: which does not
 * suit tmpfs, since it may have pages in swapcache, and needs to find those
 * for itself; although drivers/gpu/drm i915 and ttm rely upon this support.
 *
 * i915_gem_object_get_pages_gtt() mixes __GFP_NORETRY | __GFP_NOWARN in
 * with the mapping_gfp_mask(), to avoid OOMing the machine unnecessarily.
 */
struct page *shmem_read_mapping_page_gfp(struct address_space *mapping,
                                         pgoff_t index, gfp_t gfp)
{
#ifdef CONFIG_SHMEM
        struct inode *inode = mapping->host;
        struct folio *folio;
        struct page *page;
        int error;

        BUG_ON(!shmem_mapping(mapping));
        error = shmem_get_folio_gfp(inode, index, &folio, SGP_CACHE,
                                  gfp, NULL, NULL, NULL);
        if (error)
                return ERR_PTR(error);

        folio_unlock(folio);
        page = folio_file_page(folio, index);
        if (PageHWPoison(page)) {
                folio_put(folio);
                return ERR_PTR(-EIO);
        }

        return page;
#else
        /*
         * The tiny !SHMEM case uses ramfs without swap
         */
        return read_cache_page_gfp(mapping, index, gfp);
#endif
}
EXPORT_SYMBOL_GPL(shmem_read_mapping_page_gfp);