kbuild: add $(CLANG_FLAGS) to KBUILD_CPPFLAGS

[linux.git] / fs / btrfs / scrub.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2011, 2012 STRATO.  All rights reserved.
 */

#include <linux/blkdev.h>
#include <linux/ratelimit.h>
#include <linux/sched/mm.h>
#include <crypto/hash.h>
#include "ctree.h"
#include "discard.h"
#include "volumes.h"
#include "disk-io.h"
#include "ordered-data.h"
#include "transaction.h"
#include "backref.h"
#include "extent_io.h"
#include "dev-replace.h"
#include "check-integrity.h"
#include "raid56.h"
#include "block-group.h"
#include "zoned.h"
#include "fs.h"
#include "accessors.h"
#include "file-item.h"
#include "scrub.h"

/*
 * This is only the first step towards a full-features scrub. It reads all
 * extent and super block and verifies the checksums. In case a bad checksum
 * is found or the extent cannot be read, good data will be written back if
 * any can be found.
 *
 * Future enhancements:
 *  - In case an unrepairable extent is encountered, track which files are
 *    affected and report them
 *  - track and record media errors, throw out bad devices
 *  - add a mode to also read unallocated space
 */

struct scrub_ctx;

/*
 * The following value only influences the performance.
 *
 * This determines the batch size for stripe submitted in one go.
 */
#define SCRUB_STRIPES_PER_SCTX  8       /* That would be 8 64K stripe per-device. */

/*
 * The following value times PAGE_SIZE needs to be large enough to match the
 * largest node/leaf/sector size that shall be supported.
 */
#define SCRUB_MAX_SECTORS_PER_BLOCK     (BTRFS_MAX_METADATA_BLOCKSIZE / SZ_4K)

/* Represent one sector and its needed info to verify the content. */
struct scrub_sector_verification {
        bool is_metadata;

        union {
                /*
                 * Csum pointer for data csum verification.  Should point to a
                 * sector csum inside scrub_stripe::csums.
                 *
                 * NULL if this data sector has no csum.
                 */
                u8 *csum;

                /*
                 * Extra info for metadata verification.  All sectors inside a
                 * tree block share the same generation.
                 */
                u64 generation;
        };
};

enum scrub_stripe_flags {
        /* Set when @mirror_num, @dev, @physical and @logical are set. */
        SCRUB_STRIPE_FLAG_INITIALIZED,

        /* Set when the read-repair is finished. */
        SCRUB_STRIPE_FLAG_REPAIR_DONE,

        /*
         * Set for data stripes if it's triggered from P/Q stripe.
         * During such scrub, we should not report errors in data stripes, nor
         * update the accounting.
         */
        SCRUB_STRIPE_FLAG_NO_REPORT,
};

#define SCRUB_STRIPE_PAGES              (BTRFS_STRIPE_LEN / PAGE_SIZE)

/*
 * Represent one contiguous range with a length of BTRFS_STRIPE_LEN.
 */
struct scrub_stripe {
        struct scrub_ctx *sctx;
        struct btrfs_block_group *bg;

        struct page *pages[SCRUB_STRIPE_PAGES];
        struct scrub_sector_verification *sectors;

        struct btrfs_device *dev;
        u64 logical;
        u64 physical;

        u16 mirror_num;

        /* Should be BTRFS_STRIPE_LEN / sectorsize. */
        u16 nr_sectors;

        /*
         * How many data/meta extents are in this stripe.  Only for scrub status
         * reporting purposes.
         */
        u16 nr_data_extents;
        u16 nr_meta_extents;

        atomic_t pending_io;
        wait_queue_head_t io_wait;
        wait_queue_head_t repair_wait;

        /*
         * Indicate the states of the stripe.  Bits are defined in
         * scrub_stripe_flags enum.
         */
        unsigned long state;

        /* Indicate which sectors are covered by extent items. */
        unsigned long extent_sector_bitmap;

        /*
         * The errors hit during the initial read of the stripe.
         *
         * Would be utilized for error reporting and repair.
         */
        unsigned long init_error_bitmap;

        /*
         * The following error bitmaps are all for the current status.
         * Every time we submit a new read, these bitmaps may be updated.
         *
         * error_bitmap = io_error_bitmap | csum_error_bitmap | meta_error_bitmap;
         *
         * IO and csum errors can happen for both metadata and data.
         */
        unsigned long error_bitmap;
        unsigned long io_error_bitmap;
        unsigned long csum_error_bitmap;
        unsigned long meta_error_bitmap;

        /* For writeback (repair or replace) error reporting. */
        unsigned long write_error_bitmap;

        /* Writeback can be concurrent, thus we need to protect the bitmap. */
        spinlock_t write_error_lock;

        /*
         * Checksum for the whole stripe if this stripe is inside a data block
         * group.
         */
        u8 *csums;

        struct work_struct work;
};

struct scrub_ctx {
        struct scrub_stripe     stripes[SCRUB_STRIPES_PER_SCTX];
        struct scrub_stripe     *raid56_data_stripes;
        struct btrfs_fs_info    *fs_info;
        int                     first_free;
        int                     cur_stripe;
        struct list_head        csum_list;
        atomic_t                cancel_req;
        int                     readonly;
        int                     sectors_per_bio;

        /* State of IO submission throttling affecting the associated device */
        ktime_t                 throttle_deadline;
        u64                     throttle_sent;

        int                     is_dev_replace;
        u64                     write_pointer;

        struct mutex            wr_lock;
        struct btrfs_device     *wr_tgtdev;

        /*
         * statistics
         */
        struct btrfs_scrub_progress stat;
        spinlock_t              stat_lock;

        /*
         * Use a ref counter to avoid use-after-free issues. Scrub workers
         * decrement bios_in_flight and workers_pending and then do a wakeup
         * on the list_wait wait queue. We must ensure the main scrub task
         * doesn't free the scrub context before or while the workers are
         * doing the wakeup() call.
         */
        refcount_t              refs;
};

struct scrub_warning {
        struct btrfs_path       *path;
        u64                     extent_item_size;
        const char              *errstr;
        u64                     physical;
        u64                     logical;
        struct btrfs_device     *dev;
};

static void release_scrub_stripe(struct scrub_stripe *stripe)
{
        if (!stripe)
                return;

        for (int i = 0; i < SCRUB_STRIPE_PAGES; i++) {
                if (stripe->pages[i])
                        __free_page(stripe->pages[i]);
                stripe->pages[i] = NULL;
        }
        kfree(stripe->sectors);
        kfree(stripe->csums);
        stripe->sectors = NULL;
        stripe->csums = NULL;
        stripe->sctx = NULL;
        stripe->state = 0;
}

static int init_scrub_stripe(struct btrfs_fs_info *fs_info,
                             struct scrub_stripe *stripe)
{
        int ret;

        memset(stripe, 0, sizeof(*stripe));

        stripe->nr_sectors = BTRFS_STRIPE_LEN >> fs_info->sectorsize_bits;
        stripe->state = 0;

        init_waitqueue_head(&stripe->io_wait);
        init_waitqueue_head(&stripe->repair_wait);
        atomic_set(&stripe->pending_io, 0);
        spin_lock_init(&stripe->write_error_lock);

        ret = btrfs_alloc_page_array(SCRUB_STRIPE_PAGES, stripe->pages);
        if (ret < 0)
                goto error;

        stripe->sectors = kcalloc(stripe->nr_sectors,
                                  sizeof(struct scrub_sector_verification),
                                  GFP_KERNEL);
        if (!stripe->sectors)
                goto error;

        stripe->csums = kcalloc(BTRFS_STRIPE_LEN >> fs_info->sectorsize_bits,
                                fs_info->csum_size, GFP_KERNEL);
        if (!stripe->csums)
                goto error;
        return 0;
error:
        release_scrub_stripe(stripe);
        return -ENOMEM;
}

static void wait_scrub_stripe_io(struct scrub_stripe *stripe)
{
        wait_event(stripe->io_wait, atomic_read(&stripe->pending_io) == 0);
}

static void scrub_put_ctx(struct scrub_ctx *sctx);

static void __scrub_blocked_if_needed(struct btrfs_fs_info *fs_info)
{
        while (atomic_read(&fs_info->scrub_pause_req)) {
                mutex_unlock(&fs_info->scrub_lock);
                wait_event(fs_info->scrub_pause_wait,
                   atomic_read(&fs_info->scrub_pause_req) == 0);
                mutex_lock(&fs_info->scrub_lock);
        }
}

static void scrub_pause_on(struct btrfs_fs_info *fs_info)
{
        atomic_inc(&fs_info->scrubs_paused);
        wake_up(&fs_info->scrub_pause_wait);
}

static void scrub_pause_off(struct btrfs_fs_info *fs_info)
{
        mutex_lock(&fs_info->scrub_lock);
        __scrub_blocked_if_needed(fs_info);
        atomic_dec(&fs_info->scrubs_paused);
        mutex_unlock(&fs_info->scrub_lock);

        wake_up(&fs_info->scrub_pause_wait);
}

static void scrub_blocked_if_needed(struct btrfs_fs_info *fs_info)
{
        scrub_pause_on(fs_info);
        scrub_pause_off(fs_info);
}

static void scrub_free_csums(struct scrub_ctx *sctx)
{
        while (!list_empty(&sctx->csum_list)) {
                struct btrfs_ordered_sum *sum;
                sum = list_first_entry(&sctx->csum_list,
                                       struct btrfs_ordered_sum, list);
                list_del(&sum->list);
                kfree(sum);
        }
}

static noinline_for_stack void scrub_free_ctx(struct scrub_ctx *sctx)
{
        int i;

        if (!sctx)
                return;

        for (i = 0; i < SCRUB_STRIPES_PER_SCTX; i++)
                release_scrub_stripe(&sctx->stripes[i]);

        scrub_free_csums(sctx);
        kfree(sctx);
}

static void scrub_put_ctx(struct scrub_ctx *sctx)
{
        if (refcount_dec_and_test(&sctx->refs))
                scrub_free_ctx(sctx);
}

static noinline_for_stack struct scrub_ctx *scrub_setup_ctx(
                struct btrfs_fs_info *fs_info, int is_dev_replace)
{
        struct scrub_ctx *sctx;
        int             i;

        sctx = kzalloc(sizeof(*sctx), GFP_KERNEL);
        if (!sctx)
                goto nomem;
        refcount_set(&sctx->refs, 1);
        sctx->is_dev_replace = is_dev_replace;
        sctx->fs_info = fs_info;
        INIT_LIST_HEAD(&sctx->csum_list);
        for (i = 0; i < SCRUB_STRIPES_PER_SCTX; i++) {
                int ret;

                ret = init_scrub_stripe(fs_info, &sctx->stripes[i]);
                if (ret < 0)
                        goto nomem;
                sctx->stripes[i].sctx = sctx;
        }
        sctx->first_free = 0;
        atomic_set(&sctx->cancel_req, 0);

        spin_lock_init(&sctx->stat_lock);
        sctx->throttle_deadline = 0;

        mutex_init(&sctx->wr_lock);
        if (is_dev_replace) {
                WARN_ON(!fs_info->dev_replace.tgtdev);
                sctx->wr_tgtdev = fs_info->dev_replace.tgtdev;
        }

        return sctx;

nomem:
        scrub_free_ctx(sctx);
        return ERR_PTR(-ENOMEM);
}

static int scrub_print_warning_inode(u64 inum, u64 offset, u64 num_bytes,
                                     u64 root, void *warn_ctx)
{
        u32 nlink;
        int ret;
        int i;
        unsigned nofs_flag;
        struct extent_buffer *eb;
        struct btrfs_inode_item *inode_item;
        struct scrub_warning *swarn = warn_ctx;
        struct btrfs_fs_info *fs_info = swarn->dev->fs_info;
        struct inode_fs_paths *ipath = NULL;
        struct btrfs_root *local_root;
        struct btrfs_key key;

        local_root = btrfs_get_fs_root(fs_info, root, true);
        if (IS_ERR(local_root)) {
                ret = PTR_ERR(local_root);
                goto err;
        }

        /*
         * this makes the path point to (inum INODE_ITEM ioff)
         */
        key.objectid = inum;
        key.type = BTRFS_INODE_ITEM_KEY;
        key.offset = 0;

        ret = btrfs_search_slot(NULL, local_root, &key, swarn->path, 0, 0);
        if (ret) {
                btrfs_put_root(local_root);
                btrfs_release_path(swarn->path);
                goto err;
        }

        eb = swarn->path->nodes[0];
        inode_item = btrfs_item_ptr(eb, swarn->path->slots[0],
                                        struct btrfs_inode_item);
        nlink = btrfs_inode_nlink(eb, inode_item);
        btrfs_release_path(swarn->path);

        /*
         * init_path might indirectly call vmalloc, or use GFP_KERNEL. Scrub
         * uses GFP_NOFS in this context, so we keep it consistent but it does
         * not seem to be strictly necessary.
         */
        nofs_flag = memalloc_nofs_save();
        ipath = init_ipath(4096, local_root, swarn->path);
        memalloc_nofs_restore(nofs_flag);
        if (IS_ERR(ipath)) {
                btrfs_put_root(local_root);
                ret = PTR_ERR(ipath);
                ipath = NULL;
                goto err;
        }
        ret = paths_from_inode(inum, ipath);

        if (ret < 0)
                goto err;

        /*
         * we deliberately ignore the bit ipath might have been too small to
         * hold all of the paths here
         */
        for (i = 0; i < ipath->fspath->elem_cnt; ++i)
                btrfs_warn_in_rcu(fs_info,
"%s at logical %llu on dev %s, physical %llu, root %llu, inode %llu, offset %llu, length %u, links %u (path: %s)",
                                  swarn->errstr, swarn->logical,
                                  btrfs_dev_name(swarn->dev),
                                  swarn->physical,
                                  root, inum, offset,
                                  fs_info->sectorsize, nlink,
                                  (char *)(unsigned long)ipath->fspath->val[i]);

        btrfs_put_root(local_root);
        free_ipath(ipath);
        return 0;

err:
        btrfs_warn_in_rcu(fs_info,
                          "%s at logical %llu on dev %s, physical %llu, root %llu, inode %llu, offset %llu: path resolving failed with ret=%d",
                          swarn->errstr, swarn->logical,
                          btrfs_dev_name(swarn->dev),
                          swarn->physical,
                          root, inum, offset, ret);

        free_ipath(ipath);
        return 0;
}

static void scrub_print_common_warning(const char *errstr, struct btrfs_device *dev,
                                       bool is_super, u64 logical, u64 physical)
{
        struct btrfs_fs_info *fs_info = dev->fs_info;
        struct btrfs_path *path;
        struct btrfs_key found_key;
        struct extent_buffer *eb;
        struct btrfs_extent_item *ei;
        struct scrub_warning swarn;
        unsigned long ptr = 0;
        u64 flags = 0;
        u64 ref_root;
        u32 item_size;
        u8 ref_level = 0;
        int ret;

        /* Super block error, no need to search extent tree. */
        if (is_super) {
                btrfs_warn_in_rcu(fs_info, "%s on device %s, physical %llu",
                                  errstr, btrfs_dev_name(dev), physical);
                return;
        }
        path = btrfs_alloc_path();
        if (!path)
                return;

        swarn.physical = physical;
        swarn.logical = logical;
        swarn.errstr = errstr;
        swarn.dev = NULL;

        ret = extent_from_logical(fs_info, swarn.logical, path, &found_key,
                                  &flags);
        if (ret < 0)
                goto out;

        swarn.extent_item_size = found_key.offset;

        eb = path->nodes[0];
        ei = btrfs_item_ptr(eb, path->slots[0], struct btrfs_extent_item);
        item_size = btrfs_item_size(eb, path->slots[0]);

        if (flags & BTRFS_EXTENT_FLAG_TREE_BLOCK) {
                do {
                        ret = tree_backref_for_extent(&ptr, eb, &found_key, ei,
                                                      item_size, &ref_root,
                                                      &ref_level);
                        btrfs_warn_in_rcu(fs_info,
"%s at logical %llu on dev %s, physical %llu: metadata %s (level %d) in tree %llu",
                                errstr, swarn.logical,
                                btrfs_dev_name(dev),
                                swarn.physical,
                                ref_level ? "node" : "leaf",
                                ret < 0 ? -1 : ref_level,
                                ret < 0 ? -1 : ref_root);
                } while (ret != 1);
                btrfs_release_path(path);
        } else {
                struct btrfs_backref_walk_ctx ctx = { 0 };

                btrfs_release_path(path);

                ctx.bytenr = found_key.objectid;
                ctx.extent_item_pos = swarn.logical - found_key.objectid;
                ctx.fs_info = fs_info;

                swarn.path = path;
                swarn.dev = dev;

                iterate_extent_inodes(&ctx, true, scrub_print_warning_inode, &swarn);
        }

out:
        btrfs_free_path(path);
}

static inline int scrub_nr_raid_mirrors(struct btrfs_io_context *bioc)
{
        if (bioc->map_type & BTRFS_BLOCK_GROUP_RAID5)
                return 2;
        else if (bioc->map_type & BTRFS_BLOCK_GROUP_RAID6)
                return 3;
        else
                return (int)bioc->num_stripes;
}

static inline void scrub_stripe_index_and_offset(u64 logical, u64 map_type,
                                                 u64 full_stripe_logical,
                                                 int nstripes, int mirror,
                                                 int *stripe_index,
                                                 u64 *stripe_offset)
{
        int i;

        if (map_type & BTRFS_BLOCK_GROUP_RAID56_MASK) {
                const int nr_data_stripes = (map_type & BTRFS_BLOCK_GROUP_RAID5) ?
                                            nstripes - 1 : nstripes - 2;

                /* RAID5/6 */
                for (i = 0; i < nr_data_stripes; i++) {
                        const u64 data_stripe_start = full_stripe_logical +
                                                (i * BTRFS_STRIPE_LEN);

                        if (logical >= data_stripe_start &&
                            logical < data_stripe_start + BTRFS_STRIPE_LEN)
                                break;
                }

                *stripe_index = i;
                *stripe_offset = (logical - full_stripe_logical) &
                                 BTRFS_STRIPE_LEN_MASK;
        } else {
                /* The other RAID type */
                *stripe_index = mirror;
                *stripe_offset = 0;
        }
}

static int fill_writer_pointer_gap(struct scrub_ctx *sctx, u64 physical)
{
        int ret = 0;
        u64 length;

        if (!btrfs_is_zoned(sctx->fs_info))
                return 0;

        if (!btrfs_dev_is_sequential(sctx->wr_tgtdev, physical))
                return 0;

        if (sctx->write_pointer < physical) {
                length = physical - sctx->write_pointer;

                ret = btrfs_zoned_issue_zeroout(sctx->wr_tgtdev,
                                                sctx->write_pointer, length);
                if (!ret)
                        sctx->write_pointer = physical;
        }
        return ret;
}

static struct page *scrub_stripe_get_page(struct scrub_stripe *stripe, int sector_nr)
{
        struct btrfs_fs_info *fs_info = stripe->bg->fs_info;
        int page_index = (sector_nr << fs_info->sectorsize_bits) >> PAGE_SHIFT;

        return stripe->pages[page_index];
}

static unsigned int scrub_stripe_get_page_offset(struct scrub_stripe *stripe,
                                                 int sector_nr)
{
        struct btrfs_fs_info *fs_info = stripe->bg->fs_info;

        return offset_in_page(sector_nr << fs_info->sectorsize_bits);
}

static void scrub_verify_one_metadata(struct scrub_stripe *stripe, int sector_nr)
{
        struct btrfs_fs_info *fs_info = stripe->bg->fs_info;
        const u32 sectors_per_tree = fs_info->nodesize >> fs_info->sectorsize_bits;
        const u64 logical = stripe->logical + (sector_nr << fs_info->sectorsize_bits);
        const struct page *first_page = scrub_stripe_get_page(stripe, sector_nr);
        const unsigned int first_off = scrub_stripe_get_page_offset(stripe, sector_nr);
        SHASH_DESC_ON_STACK(shash, fs_info->csum_shash);
        u8 on_disk_csum[BTRFS_CSUM_SIZE];
        u8 calculated_csum[BTRFS_CSUM_SIZE];
        struct btrfs_header *header;

        /*
         * Here we don't have a good way to attach the pages (and subpages)
         * to a dummy extent buffer, thus we have to directly grab the members
         * from pages.
         */
        header = (struct btrfs_header *)(page_address(first_page) + first_off);
        memcpy(on_disk_csum, header->csum, fs_info->csum_size);

        if (logical != btrfs_stack_header_bytenr(header)) {
                bitmap_set(&stripe->csum_error_bitmap, sector_nr, sectors_per_tree);
                bitmap_set(&stripe->error_bitmap, sector_nr, sectors_per_tree);
                btrfs_warn_rl(fs_info,
                "tree block %llu mirror %u has bad bytenr, has %llu want %llu",
                              logical, stripe->mirror_num,
                              btrfs_stack_header_bytenr(header), logical);
                return;
        }
        if (memcmp(header->fsid, fs_info->fs_devices->fsid, BTRFS_FSID_SIZE) != 0) {
                bitmap_set(&stripe->meta_error_bitmap, sector_nr, sectors_per_tree);
                bitmap_set(&stripe->error_bitmap, sector_nr, sectors_per_tree);
                btrfs_warn_rl(fs_info,
                "tree block %llu mirror %u has bad fsid, has %pU want %pU",
                              logical, stripe->mirror_num,
                              header->fsid, fs_info->fs_devices->fsid);
                return;
        }
        if (memcmp(header->chunk_tree_uuid, fs_info->chunk_tree_uuid,
                   BTRFS_UUID_SIZE) != 0) {
                bitmap_set(&stripe->meta_error_bitmap, sector_nr, sectors_per_tree);
                bitmap_set(&stripe->error_bitmap, sector_nr, sectors_per_tree);
                btrfs_warn_rl(fs_info,
                "tree block %llu mirror %u has bad chunk tree uuid, has %pU want %pU",
                              logical, stripe->mirror_num,
                              header->chunk_tree_uuid, fs_info->chunk_tree_uuid);
                return;
        }

        /* Now check tree block csum. */
        shash->tfm = fs_info->csum_shash;
        crypto_shash_init(shash);
        crypto_shash_update(shash, page_address(first_page) + first_off +
                            BTRFS_CSUM_SIZE, fs_info->sectorsize - BTRFS_CSUM_SIZE);

        for (int i = sector_nr + 1; i < sector_nr + sectors_per_tree; i++) {
                struct page *page = scrub_stripe_get_page(stripe, i);
                unsigned int page_off = scrub_stripe_get_page_offset(stripe, i);

                crypto_shash_update(shash, page_address(page) + page_off,
                                    fs_info->sectorsize);
        }

        crypto_shash_final(shash, calculated_csum);
        if (memcmp(calculated_csum, on_disk_csum, fs_info->csum_size) != 0) {
                bitmap_set(&stripe->meta_error_bitmap, sector_nr, sectors_per_tree);
                bitmap_set(&stripe->error_bitmap, sector_nr, sectors_per_tree);
                btrfs_warn_rl(fs_info,
                "tree block %llu mirror %u has bad csum, has " CSUM_FMT " want " CSUM_FMT,
                              logical, stripe->mirror_num,
                              CSUM_FMT_VALUE(fs_info->csum_size, on_disk_csum),
                              CSUM_FMT_VALUE(fs_info->csum_size, calculated_csum));
                return;
        }
        if (stripe->sectors[sector_nr].generation !=
            btrfs_stack_header_generation(header)) {
                bitmap_set(&stripe->meta_error_bitmap, sector_nr, sectors_per_tree);
                bitmap_set(&stripe->error_bitmap, sector_nr, sectors_per_tree);
                btrfs_warn_rl(fs_info,
                "tree block %llu mirror %u has bad generation, has %llu want %llu",
                              logical, stripe->mirror_num,
                              btrfs_stack_header_generation(header),
                              stripe->sectors[sector_nr].generation);
                return;
        }
        bitmap_clear(&stripe->error_bitmap, sector_nr, sectors_per_tree);
        bitmap_clear(&stripe->csum_error_bitmap, sector_nr, sectors_per_tree);
        bitmap_clear(&stripe->meta_error_bitmap, sector_nr, sectors_per_tree);
}

static void scrub_verify_one_sector(struct scrub_stripe *stripe, int sector_nr)
{
        struct btrfs_fs_info *fs_info = stripe->bg->fs_info;
        struct scrub_sector_verification *sector = &stripe->sectors[sector_nr];
        const u32 sectors_per_tree = fs_info->nodesize >> fs_info->sectorsize_bits;
        struct page *page = scrub_stripe_get_page(stripe, sector_nr);
        unsigned int pgoff = scrub_stripe_get_page_offset(stripe, sector_nr);
        u8 csum_buf[BTRFS_CSUM_SIZE];
        int ret;

        ASSERT(sector_nr >= 0 && sector_nr < stripe->nr_sectors);

        /* Sector not utilized, skip it. */
        if (!test_bit(sector_nr, &stripe->extent_sector_bitmap))
                return;

        /* IO error, no need to check. */
        if (test_bit(sector_nr, &stripe->io_error_bitmap))
                return;

        /* Metadata, verify the full tree block. */
        if (sector->is_metadata) {
                /*
                 * Check if the tree block crosses the stripe boudary.  If
                 * crossed the boundary, we cannot verify it but only give a
                 * warning.
                 *
                 * This can only happen on a very old filesystem where chunks
                 * are not ensured to be stripe aligned.
                 */
                if (unlikely(sector_nr + sectors_per_tree > stripe->nr_sectors)) {
                        btrfs_warn_rl(fs_info,
                        "tree block at %llu crosses stripe boundary %llu",
                                      stripe->logical +
                                      (sector_nr << fs_info->sectorsize_bits),
                                      stripe->logical);
                        return;
                }
                scrub_verify_one_metadata(stripe, sector_nr);
                return;
        }

        /*
         * Data is easier, we just verify the data csum (if we have it).  For
         * cases without csum, we have no other choice but to trust it.
         */
        if (!sector->csum) {
                clear_bit(sector_nr, &stripe->error_bitmap);
                return;
        }

        ret = btrfs_check_sector_csum(fs_info, page, pgoff, csum_buf, sector->csum);
        if (ret < 0) {
                set_bit(sector_nr, &stripe->csum_error_bitmap);
                set_bit(sector_nr, &stripe->error_bitmap);
        } else {
                clear_bit(sector_nr, &stripe->csum_error_bitmap);
                clear_bit(sector_nr, &stripe->error_bitmap);
        }
}

/* Verify specified sectors of a stripe. */
static void scrub_verify_one_stripe(struct scrub_stripe *stripe, unsigned long bitmap)
{
        struct btrfs_fs_info *fs_info = stripe->bg->fs_info;
        const u32 sectors_per_tree = fs_info->nodesize >> fs_info->sectorsize_bits;
        int sector_nr;

        for_each_set_bit(sector_nr, &bitmap, stripe->nr_sectors) {
                scrub_verify_one_sector(stripe, sector_nr);
                if (stripe->sectors[sector_nr].is_metadata)
                        sector_nr += sectors_per_tree - 1;
        }
}

static int calc_sector_number(struct scrub_stripe *stripe, struct bio_vec *first_bvec)
{
        int i;

        for (i = 0; i < stripe->nr_sectors; i++) {
                if (scrub_stripe_get_page(stripe, i) == first_bvec->bv_page &&
                    scrub_stripe_get_page_offset(stripe, i) == first_bvec->bv_offset)
                        break;
        }
        ASSERT(i < stripe->nr_sectors);
        return i;
}

/*
 * Repair read is different to the regular read:
 *
 * - Only reads the failed sectors
 * - May have extra blocksize limits
 */
static void scrub_repair_read_endio(struct btrfs_bio *bbio)
{
        struct scrub_stripe *stripe = bbio->private;
        struct btrfs_fs_info *fs_info = stripe->bg->fs_info;
        struct bio_vec *bvec;
        int sector_nr = calc_sector_number(stripe, bio_first_bvec_all(&bbio->bio));
        u32 bio_size = 0;
        int i;

        ASSERT(sector_nr < stripe->nr_sectors);

        bio_for_each_bvec_all(bvec, &bbio->bio, i)
                bio_size += bvec->bv_len;

        if (bbio->bio.bi_status) {
                bitmap_set(&stripe->io_error_bitmap, sector_nr,
                           bio_size >> fs_info->sectorsize_bits);
                bitmap_set(&stripe->error_bitmap, sector_nr,
                           bio_size >> fs_info->sectorsize_bits);
        } else {
                bitmap_clear(&stripe->io_error_bitmap, sector_nr,
                             bio_size >> fs_info->sectorsize_bits);
        }
        bio_put(&bbio->bio);
        if (atomic_dec_and_test(&stripe->pending_io))
                wake_up(&stripe->io_wait);
}

static int calc_next_mirror(int mirror, int num_copies)
{
        ASSERT(mirror <= num_copies);
        return (mirror + 1 > num_copies) ? 1 : mirror + 1;
}

static void scrub_stripe_submit_repair_read(struct scrub_stripe *stripe,
                                            int mirror, int blocksize, bool wait)
{
        struct btrfs_fs_info *fs_info = stripe->bg->fs_info;
        struct btrfs_bio *bbio = NULL;
        const unsigned long old_error_bitmap = stripe->error_bitmap;
        int i;

        ASSERT(stripe->mirror_num >= 1);
        ASSERT(atomic_read(&stripe->pending_io) == 0);

        for_each_set_bit(i, &old_error_bitmap, stripe->nr_sectors) {
                struct page *page;
                int pgoff;
                int ret;

                page = scrub_stripe_get_page(stripe, i);
                pgoff = scrub_stripe_get_page_offset(stripe, i);

                /* The current sector cannot be merged, submit the bio. */
                if (bbio && ((i > 0 && !test_bit(i - 1, &stripe->error_bitmap)) ||
                             bbio->bio.bi_iter.bi_size >= blocksize)) {
                        ASSERT(bbio->bio.bi_iter.bi_size);
                        atomic_inc(&stripe->pending_io);
                        btrfs_submit_bio(bbio, mirror);
                        if (wait)
                                wait_scrub_stripe_io(stripe);
                        bbio = NULL;
                }

                if (!bbio) {
                        bbio = btrfs_bio_alloc(stripe->nr_sectors, REQ_OP_READ,
                                fs_info, scrub_repair_read_endio, stripe);
                        bbio->bio.bi_iter.bi_sector = (stripe->logical +
                                (i << fs_info->sectorsize_bits)) >> SECTOR_SHIFT;
                }

                ret = bio_add_page(&bbio->bio, page, fs_info->sectorsize, pgoff);
                ASSERT(ret == fs_info->sectorsize);
        }
        if (bbio) {
                ASSERT(bbio->bio.bi_iter.bi_size);
                atomic_inc(&stripe->pending_io);
                btrfs_submit_bio(bbio, mirror);
                if (wait)
                        wait_scrub_stripe_io(stripe);
        }
}

static void scrub_stripe_report_errors(struct scrub_ctx *sctx,
                                       struct scrub_stripe *stripe)
{
        static DEFINE_RATELIMIT_STATE(rs, DEFAULT_RATELIMIT_INTERVAL,
                                      DEFAULT_RATELIMIT_BURST);
        struct btrfs_fs_info *fs_info = sctx->fs_info;
        struct btrfs_device *dev = NULL;
        u64 physical = 0;
        int nr_data_sectors = 0;
        int nr_meta_sectors = 0;
        int nr_nodatacsum_sectors = 0;
        int nr_repaired_sectors = 0;
        int sector_nr;

        if (test_bit(SCRUB_STRIPE_FLAG_NO_REPORT, &stripe->state))
                return;

        /*
         * Init needed infos for error reporting.
         *
         * Although our scrub_stripe infrastucture is mostly based on btrfs_submit_bio()
         * thus no need for dev/physical, error reporting still needs dev and physical.
         */
        if (!bitmap_empty(&stripe->init_error_bitmap, stripe->nr_sectors)) {
                u64 mapped_len = fs_info->sectorsize;
                struct btrfs_io_context *bioc = NULL;
                int stripe_index = stripe->mirror_num - 1;
                int ret;

                /* For scrub, our mirror_num should always start at 1. */
                ASSERT(stripe->mirror_num >= 1);
                ret = btrfs_map_sblock(fs_info, BTRFS_MAP_GET_READ_MIRRORS,
                                       stripe->logical, &mapped_len, &bioc);
                /*
                 * If we failed, dev will be NULL, and later detailed reports
                 * will just be skipped.
                 */
                if (ret < 0)
                        goto skip;
                physical = bioc->stripes[stripe_index].physical;
                dev = bioc->stripes[stripe_index].dev;
                btrfs_put_bioc(bioc);
        }

skip:
        for_each_set_bit(sector_nr, &stripe->extent_sector_bitmap, stripe->nr_sectors) {
                bool repaired = false;

                if (stripe->sectors[sector_nr].is_metadata) {
                        nr_meta_sectors++;
                } else {
                        nr_data_sectors++;
                        if (!stripe->sectors[sector_nr].csum)
                                nr_nodatacsum_sectors++;
                }

                if (test_bit(sector_nr, &stripe->init_error_bitmap) &&
                    !test_bit(sector_nr, &stripe->error_bitmap)) {
                        nr_repaired_sectors++;
                        repaired = true;
                }

                /* Good sector from the beginning, nothing need to be done. */
                if (!test_bit(sector_nr, &stripe->init_error_bitmap))
                        continue;

                /*
                 * Report error for the corrupted sectors.  If repaired, just
                 * output the message of repaired message.
                 */
                if (repaired) {
                        if (dev) {
                                btrfs_err_rl_in_rcu(fs_info,
                        "fixed up error at logical %llu on dev %s physical %llu",
                                            stripe->logical, btrfs_dev_name(dev),
                                            physical);
                        } else {
                                btrfs_err_rl_in_rcu(fs_info,
                        "fixed up error at logical %llu on mirror %u",
                                            stripe->logical, stripe->mirror_num);
                        }
                        continue;
                }

                /* The remaining are all for unrepaired. */
                if (dev) {
                        btrfs_err_rl_in_rcu(fs_info,
        "unable to fixup (regular) error at logical %llu on dev %s physical %llu",
                                            stripe->logical, btrfs_dev_name(dev),
                                            physical);
                } else {
                        btrfs_err_rl_in_rcu(fs_info,
        "unable to fixup (regular) error at logical %llu on mirror %u",
                                            stripe->logical, stripe->mirror_num);
                }

                if (test_bit(sector_nr, &stripe->io_error_bitmap))
                        if (__ratelimit(&rs) && dev)
                                scrub_print_common_warning("i/o error", dev, false,
                                                     stripe->logical, physical);
                if (test_bit(sector_nr, &stripe->csum_error_bitmap))
                        if (__ratelimit(&rs) && dev)
                                scrub_print_common_warning("checksum error", dev, false,
                                                     stripe->logical, physical);
                if (test_bit(sector_nr, &stripe->meta_error_bitmap))
                        if (__ratelimit(&rs) && dev)
                                scrub_print_common_warning("header error", dev, false,
                                                     stripe->logical, physical);
        }

        spin_lock(&sctx->stat_lock);
        sctx->stat.data_extents_scrubbed += stripe->nr_data_extents;
        sctx->stat.tree_extents_scrubbed += stripe->nr_meta_extents;
        sctx->stat.data_bytes_scrubbed += nr_data_sectors << fs_info->sectorsize_bits;
        sctx->stat.tree_bytes_scrubbed += nr_meta_sectors << fs_info->sectorsize_bits;
        sctx->stat.no_csum += nr_nodatacsum_sectors;
        sctx->stat.read_errors +=
                bitmap_weight(&stripe->io_error_bitmap, stripe->nr_sectors);
        sctx->stat.csum_errors +=
                bitmap_weight(&stripe->csum_error_bitmap, stripe->nr_sectors);
        sctx->stat.verify_errors +=
                bitmap_weight(&stripe->meta_error_bitmap, stripe->nr_sectors);
        sctx->stat.uncorrectable_errors +=
                bitmap_weight(&stripe->error_bitmap, stripe->nr_sectors);
        sctx->stat.corrected_errors += nr_repaired_sectors;
        spin_unlock(&sctx->stat_lock);
}

/*
 * The main entrance for all read related scrub work, including:
 *
 * - Wait for the initial read to finish
 * - Verify and locate any bad sectors
 * - Go through the remaining mirrors and try to read as large blocksize as
 *   possible
 * - Go through all mirrors (including the failed mirror) sector-by-sector
 *
 * Writeback does not happen here, it needs extra synchronization.
 */
static void scrub_stripe_read_repair_worker(struct work_struct *work)
{
        struct scrub_stripe *stripe = container_of(work, struct scrub_stripe, work);
        struct btrfs_fs_info *fs_info = stripe->bg->fs_info;
        int num_copies = btrfs_num_copies(fs_info, stripe->bg->start,
                                          stripe->bg->length);
        int mirror;
        int i;

        ASSERT(stripe->mirror_num > 0);

        wait_scrub_stripe_io(stripe);
        scrub_verify_one_stripe(stripe, stripe->extent_sector_bitmap);
        /* Save the initial failed bitmap for later repair and report usage. */
        stripe->init_error_bitmap = stripe->error_bitmap;

        if (bitmap_empty(&stripe->init_error_bitmap, stripe->nr_sectors))
                goto out;

        /*
         * Try all remaining mirrors.
         *
         * Here we still try to read as large block as possible, as this is
         * faster and we have extra safety nets to rely on.
         */
        for (mirror = calc_next_mirror(stripe->mirror_num, num_copies);
             mirror != stripe->mirror_num;
             mirror = calc_next_mirror(mirror, num_copies)) {
                const unsigned long old_error_bitmap = stripe->error_bitmap;

                scrub_stripe_submit_repair_read(stripe, mirror,
                                                BTRFS_STRIPE_LEN, false);
                wait_scrub_stripe_io(stripe);
                scrub_verify_one_stripe(stripe, old_error_bitmap);
                if (bitmap_empty(&stripe->error_bitmap, stripe->nr_sectors))
                        goto out;
        }

        /*
         * Last safety net, try re-checking all mirrors, including the failed
         * one, sector-by-sector.
         *
         * As if one sector failed the drive's internal csum, the whole read
         * containing the offending sector would be marked as error.
         * Thus here we do sector-by-sector read.
         *
         * This can be slow, thus we only try it as the last resort.
         */

        for (i = 0, mirror = stripe->mirror_num;
             i < num_copies;
             i++, mirror = calc_next_mirror(mirror, num_copies)) {
                const unsigned long old_error_bitmap = stripe->error_bitmap;

                scrub_stripe_submit_repair_read(stripe, mirror,
                                                fs_info->sectorsize, true);
                wait_scrub_stripe_io(stripe);
                scrub_verify_one_stripe(stripe, old_error_bitmap);
                if (bitmap_empty(&stripe->error_bitmap, stripe->nr_sectors))
                        goto out;
        }
out:
        scrub_stripe_report_errors(stripe->sctx, stripe);
        set_bit(SCRUB_STRIPE_FLAG_REPAIR_DONE, &stripe->state);
        wake_up(&stripe->repair_wait);
}

static void scrub_read_endio(struct btrfs_bio *bbio)
{
        struct scrub_stripe *stripe = bbio->private;

        if (bbio->bio.bi_status) {
                bitmap_set(&stripe->io_error_bitmap, 0, stripe->nr_sectors);
                bitmap_set(&stripe->error_bitmap, 0, stripe->nr_sectors);
        } else {
                bitmap_clear(&stripe->io_error_bitmap, 0, stripe->nr_sectors);
        }
        bio_put(&bbio->bio);
        if (atomic_dec_and_test(&stripe->pending_io)) {
                wake_up(&stripe->io_wait);
                INIT_WORK(&stripe->work, scrub_stripe_read_repair_worker);
                queue_work(stripe->bg->fs_info->scrub_workers, &stripe->work);
        }
}

static void scrub_write_endio(struct btrfs_bio *bbio)
{
        struct scrub_stripe *stripe = bbio->private;
        struct btrfs_fs_info *fs_info = stripe->bg->fs_info;
        struct bio_vec *bvec;
        int sector_nr = calc_sector_number(stripe, bio_first_bvec_all(&bbio->bio));
        u32 bio_size = 0;
        int i;

        bio_for_each_bvec_all(bvec, &bbio->bio, i)
                bio_size += bvec->bv_len;

        if (bbio->bio.bi_status) {
                unsigned long flags;

                spin_lock_irqsave(&stripe->write_error_lock, flags);
                bitmap_set(&stripe->write_error_bitmap, sector_nr,
                           bio_size >> fs_info->sectorsize_bits);
                spin_unlock_irqrestore(&stripe->write_error_lock, flags);
        }
        bio_put(&bbio->bio);

        if (atomic_dec_and_test(&stripe->pending_io))
                wake_up(&stripe->io_wait);
}

/*
 * Submit the write bio(s) for the sectors specified by @write_bitmap.
 *
 * Here we utilize btrfs_submit_repair_write(), which has some extra benefits:
 *
 * - Only needs logical bytenr and mirror_num
 *   Just like the scrub read path
 *
 * - Would only result in writes to the specified mirror
 *   Unlike the regular writeback path, which would write back to all stripes
 *
 * - Handle dev-replace and read-repair writeback differently
 */
static void scrub_write_sectors(struct scrub_ctx *sctx, struct scrub_stripe *stripe,
                                unsigned long write_bitmap, bool dev_replace)
{
        struct btrfs_fs_info *fs_info = stripe->bg->fs_info;
        struct btrfs_bio *bbio = NULL;
        const bool zoned = btrfs_is_zoned(fs_info);
        int sector_nr;

        for_each_set_bit(sector_nr, &write_bitmap, stripe->nr_sectors) {
                struct page *page = scrub_stripe_get_page(stripe, sector_nr);
                unsigned int pgoff = scrub_stripe_get_page_offset(stripe, sector_nr);
                int ret;

                /* We should only writeback sectors covered by an extent. */
                ASSERT(test_bit(sector_nr, &stripe->extent_sector_bitmap));

                /* Cannot merge with previous sector, submit the current one. */
                if (bbio && sector_nr && !test_bit(sector_nr - 1, &write_bitmap)) {
                        fill_writer_pointer_gap(sctx, stripe->physical +
                                        (sector_nr << fs_info->sectorsize_bits));
                        atomic_inc(&stripe->pending_io);
                        btrfs_submit_repair_write(bbio, stripe->mirror_num, dev_replace);
                        /* For zoned writeback, queue depth must be 1. */
                        if (zoned)
                                wait_scrub_stripe_io(stripe);
                        bbio = NULL;
                }
                if (!bbio) {
                        bbio = btrfs_bio_alloc(stripe->nr_sectors, REQ_OP_WRITE,
                                               fs_info, scrub_write_endio, stripe);
                        bbio->bio.bi_iter.bi_sector = (stripe->logical +
                                (sector_nr << fs_info->sectorsize_bits)) >>
                                SECTOR_SHIFT;
                }
                ret = bio_add_page(&bbio->bio, page, fs_info->sectorsize, pgoff);
                ASSERT(ret == fs_info->sectorsize);
        }
        if (bbio) {
                fill_writer_pointer_gap(sctx, bbio->bio.bi_iter.bi_sector <<
                                        SECTOR_SHIFT);
                atomic_inc(&stripe->pending_io);
                btrfs_submit_repair_write(bbio, stripe->mirror_num, dev_replace);
                if (zoned)
                        wait_scrub_stripe_io(stripe);
        }
}

/*
 * Throttling of IO submission, bandwidth-limit based, the timeslice is 1
 * second.  Limit can be set via /sys/fs/UUID/devinfo/devid/scrub_speed_max.
 */
static void scrub_throttle_dev_io(struct scrub_ctx *sctx, struct btrfs_device *device,
                                  unsigned int bio_size)
{
        const int time_slice = 1000;
        s64 delta;
        ktime_t now;
        u32 div;
        u64 bwlimit;

        bwlimit = READ_ONCE(device->scrub_speed_max);
        if (bwlimit == 0)
                return;

        /*
         * Slice is divided into intervals when the IO is submitted, adjust by
         * bwlimit and maximum of 64 intervals.
         */
        div = max_t(u32, 1, (u32)(bwlimit / (16 * 1024 * 1024)));
        div = min_t(u32, 64, div);

        /* Start new epoch, set deadline */
        now = ktime_get();
        if (sctx->throttle_deadline == 0) {
                sctx->throttle_deadline = ktime_add_ms(now, time_slice / div);
                sctx->throttle_sent = 0;
        }

        /* Still in the time to send? */
        if (ktime_before(now, sctx->throttle_deadline)) {
                /* If current bio is within the limit, send it */
                sctx->throttle_sent += bio_size;
                if (sctx->throttle_sent <= div_u64(bwlimit, div))
                        return;

                /* We're over the limit, sleep until the rest of the slice */
                delta = ktime_ms_delta(sctx->throttle_deadline, now);
        } else {
                /* New request after deadline, start new epoch */
                delta = 0;
        }

        if (delta) {
                long timeout;

                timeout = div_u64(delta * HZ, 1000);
                schedule_timeout_interruptible(timeout);
        }

        /* Next call will start the deadline period */
        sctx->throttle_deadline = 0;
}

/*
 * Given a physical address, this will calculate it's
 * logical offset. if this is a parity stripe, it will return
 * the most left data stripe's logical offset.
 *
 * return 0 if it is a data stripe, 1 means parity stripe.
 */
static int get_raid56_logic_offset(u64 physical, int num,
                                   struct map_lookup *map, u64 *offset,
                                   u64 *stripe_start)
{
        int i;
        int j = 0;
        u64 last_offset;
        const int data_stripes = nr_data_stripes(map);

        last_offset = (physical - map->stripes[num].physical) * data_stripes;
        if (stripe_start)
                *stripe_start = last_offset;

        *offset = last_offset;
        for (i = 0; i < data_stripes; i++) {
                u32 stripe_nr;
                u32 stripe_index;
                u32 rot;

                *offset = last_offset + (i << BTRFS_STRIPE_LEN_SHIFT);

                stripe_nr = (u32)(*offset >> BTRFS_STRIPE_LEN_SHIFT) / data_stripes;

                /* Work out the disk rotation on this stripe-set */
                rot = stripe_nr % map->num_stripes;
                stripe_nr /= map->num_stripes;
                /* calculate which stripe this data locates */
                rot += i;
                stripe_index = rot % map->num_stripes;
                if (stripe_index == num)
                        return 0;
                if (stripe_index < num)
                        j++;
        }
        *offset = last_offset + (j << BTRFS_STRIPE_LEN_SHIFT);
        return 1;
}

/*
 * Return 0 if the extent item range covers any byte of the range.
 * Return <0 if the extent item is before @search_start.
 * Return >0 if the extent item is after @start_start + @search_len.
 */
static int compare_extent_item_range(struct btrfs_path *path,
                                     u64 search_start, u64 search_len)
{
        struct btrfs_fs_info *fs_info = path->nodes[0]->fs_info;
        u64 len;
        struct btrfs_key key;

        btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
        ASSERT(key.type == BTRFS_EXTENT_ITEM_KEY ||
               key.type == BTRFS_METADATA_ITEM_KEY);
        if (key.type == BTRFS_METADATA_ITEM_KEY)
                len = fs_info->nodesize;
        else
                len = key.offset;

        if (key.objectid + len <= search_start)
                return -1;
        if (key.objectid >= search_start + search_len)
                return 1;
        return 0;
}

/*
 * Locate one extent item which covers any byte in range
 * [@search_start, @search_start + @search_length)
 *
 * If the path is not initialized, we will initialize the search by doing
 * a btrfs_search_slot().
 * If the path is already initialized, we will use the path as the initial
 * slot, to avoid duplicated btrfs_search_slot() calls.
 *
 * NOTE: If an extent item starts before @search_start, we will still
 * return the extent item. This is for data extent crossing stripe boundary.
 *
 * Return 0 if we found such extent item, and @path will point to the extent item.
 * Return >0 if no such extent item can be found, and @path will be released.
 * Return <0 if hit fatal error, and @path will be released.
 */
static int find_first_extent_item(struct btrfs_root *extent_root,
                                  struct btrfs_path *path,
                                  u64 search_start, u64 search_len)
{
        struct btrfs_fs_info *fs_info = extent_root->fs_info;
        struct btrfs_key key;
        int ret;

        /* Continue using the existing path */
        if (path->nodes[0])
                goto search_forward;

        if (btrfs_fs_incompat(fs_info, SKINNY_METADATA))
                key.type = BTRFS_METADATA_ITEM_KEY;
        else
                key.type = BTRFS_EXTENT_ITEM_KEY;
        key.objectid = search_start;
        key.offset = (u64)-1;

        ret = btrfs_search_slot(NULL, extent_root, &key, path, 0, 0);
        if (ret < 0)
                return ret;

        ASSERT(ret > 0);
        /*
         * Here we intentionally pass 0 as @min_objectid, as there could be
         * an extent item starting before @search_start.
         */
        ret = btrfs_previous_extent_item(extent_root, path, 0);
        if (ret < 0)
                return ret;
        /*
         * No matter whether we have found an extent item, the next loop will
         * properly do every check on the key.
         */
search_forward:
        while (true) {
                btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
                if (key.objectid >= search_start + search_len)
                        break;
                if (key.type != BTRFS_METADATA_ITEM_KEY &&
                    key.type != BTRFS_EXTENT_ITEM_KEY)
                        goto next;

                ret = compare_extent_item_range(path, search_start, search_len);
                if (ret == 0)
                        return ret;
                if (ret > 0)
                        break;
next:
                path->slots[0]++;
                if (path->slots[0] >= btrfs_header_nritems(path->nodes[0])) {
                        ret = btrfs_next_leaf(extent_root, path);
                        if (ret) {
                                /* Either no more item or fatal error */
                                btrfs_release_path(path);
                                return ret;
                        }
                }
        }
        btrfs_release_path(path);
        return 1;
}

static void get_extent_info(struct btrfs_path *path, u64 *extent_start_ret,
                            u64 *size_ret, u64 *flags_ret, u64 *generation_ret)
{
        struct btrfs_key key;
        struct btrfs_extent_item *ei;

        btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
        ASSERT(key.type == BTRFS_METADATA_ITEM_KEY ||
               key.type == BTRFS_EXTENT_ITEM_KEY);
        *extent_start_ret = key.objectid;
        if (key.type == BTRFS_METADATA_ITEM_KEY)
                *size_ret = path->nodes[0]->fs_info->nodesize;
        else
                *size_ret = key.offset;
        ei = btrfs_item_ptr(path->nodes[0], path->slots[0], struct btrfs_extent_item);
        *flags_ret = btrfs_extent_flags(path->nodes[0], ei);
        *generation_ret = btrfs_extent_generation(path->nodes[0], ei);
}

static int sync_write_pointer_for_zoned(struct scrub_ctx *sctx, u64 logical,
                                        u64 physical, u64 physical_end)
{
        struct btrfs_fs_info *fs_info = sctx->fs_info;
        int ret = 0;

        if (!btrfs_is_zoned(fs_info))
                return 0;

        mutex_lock(&sctx->wr_lock);
        if (sctx->write_pointer < physical_end) {
                ret = btrfs_sync_zone_write_pointer(sctx->wr_tgtdev, logical,
                                                    physical,
                                                    sctx->write_pointer);
                if (ret)
                        btrfs_err(fs_info,
                                  "zoned: failed to recover write pointer");
        }
        mutex_unlock(&sctx->wr_lock);
        btrfs_dev_clear_zone_empty(sctx->wr_tgtdev, physical);

        return ret;
}

static void fill_one_extent_info(struct btrfs_fs_info *fs_info,
                                 struct scrub_stripe *stripe,
                                 u64 extent_start, u64 extent_len,
                                 u64 extent_flags, u64 extent_gen)
{
        for (u64 cur_logical = max(stripe->logical, extent_start);
             cur_logical < min(stripe->logical + BTRFS_STRIPE_LEN,
                               extent_start + extent_len);
             cur_logical += fs_info->sectorsize) {
                const int nr_sector = (cur_logical - stripe->logical) >>
                                      fs_info->sectorsize_bits;
                struct scrub_sector_verification *sector =
                                                &stripe->sectors[nr_sector];

                set_bit(nr_sector, &stripe->extent_sector_bitmap);
                if (extent_flags & BTRFS_EXTENT_FLAG_TREE_BLOCK) {
                        sector->is_metadata = true;
                        sector->generation = extent_gen;
                }
        }
}

static void scrub_stripe_reset_bitmaps(struct scrub_stripe *stripe)
{
        stripe->extent_sector_bitmap = 0;
        stripe->init_error_bitmap = 0;
        stripe->error_bitmap = 0;
        stripe->io_error_bitmap = 0;
        stripe->csum_error_bitmap = 0;
        stripe->meta_error_bitmap = 0;
}

/*
 * Locate one stripe which has at least one extent in its range.
 *
 * Return 0 if found such stripe, and store its info into @stripe.
 * Return >0 if there is no such stripe in the specified range.
 * Return <0 for error.
 */
static int scrub_find_fill_first_stripe(struct btrfs_block_group *bg,
                                        struct btrfs_device *dev, u64 physical,
                                        int mirror_num, u64 logical_start,
                                        u32 logical_len,
                                        struct scrub_stripe *stripe)
{
        struct btrfs_fs_info *fs_info = bg->fs_info;
        struct btrfs_root *extent_root = btrfs_extent_root(fs_info, bg->start);
        struct btrfs_root *csum_root = btrfs_csum_root(fs_info, bg->start);
        const u64 logical_end = logical_start + logical_len;
        struct btrfs_path path = { 0 };
        u64 cur_logical = logical_start;
        u64 stripe_end;
        u64 extent_start;
        u64 extent_len;
        u64 extent_flags;
        u64 extent_gen;
        int ret;

        memset(stripe->sectors, 0, sizeof(struct scrub_sector_verification) *
                                   stripe->nr_sectors);
        scrub_stripe_reset_bitmaps(stripe);

        /* The range must be inside the bg. */
        ASSERT(logical_start >= bg->start && logical_end <= bg->start + bg->length);

        path.search_commit_root = 1;
        path.skip_locking = 1;

        ret = find_first_extent_item(extent_root, &path, logical_start, logical_len);
        /* Either error or not found. */
        if (ret)
                goto out;
        get_extent_info(&path, &extent_start, &extent_len, &extent_flags, &extent_gen);
        if (extent_flags & BTRFS_EXTENT_FLAG_TREE_BLOCK)
                stripe->nr_meta_extents++;
        if (extent_flags & BTRFS_EXTENT_FLAG_DATA)
                stripe->nr_data_extents++;
        cur_logical = max(extent_start, cur_logical);

        /*
         * Round down to stripe boundary.
         *
         * The extra calculation against bg->start is to handle block groups
         * whose logical bytenr is not BTRFS_STRIPE_LEN aligned.
         */
        stripe->logical = round_down(cur_logical - bg->start, BTRFS_STRIPE_LEN) +
                          bg->start;
        stripe->physical = physical + stripe->logical - logical_start;
        stripe->dev = dev;
        stripe->bg = bg;
        stripe->mirror_num = mirror_num;
        stripe_end = stripe->logical + BTRFS_STRIPE_LEN - 1;

        /* Fill the first extent info into stripe->sectors[] array. */
        fill_one_extent_info(fs_info, stripe, extent_start, extent_len,
                             extent_flags, extent_gen);
        cur_logical = extent_start + extent_len;

        /* Fill the extent info for the remaining sectors. */
        while (cur_logical <= stripe_end) {
                ret = find_first_extent_item(extent_root, &path, cur_logical,
                                             stripe_end - cur_logical + 1);
                if (ret < 0)
                        goto out;
                if (ret > 0) {
                        ret = 0;
                        break;
                }
                get_extent_info(&path, &extent_start, &extent_len,
                                &extent_flags, &extent_gen);
                if (extent_flags & BTRFS_EXTENT_FLAG_TREE_BLOCK)
                        stripe->nr_meta_extents++;
                if (extent_flags & BTRFS_EXTENT_FLAG_DATA)
                        stripe->nr_data_extents++;
                fill_one_extent_info(fs_info, stripe, extent_start, extent_len,
                                     extent_flags, extent_gen);
                cur_logical = extent_start + extent_len;
        }

        /* Now fill the data csum. */
        if (bg->flags & BTRFS_BLOCK_GROUP_DATA) {
                int sector_nr;
                unsigned long csum_bitmap = 0;

                /* Csum space should have already been allocated. */
                ASSERT(stripe->csums);

                /*
                 * Our csum bitmap should be large enough, as BTRFS_STRIPE_LEN
                 * should contain at most 16 sectors.
                 */
                ASSERT(BITS_PER_LONG >= BTRFS_STRIPE_LEN >> fs_info->sectorsize_bits);

                ret = btrfs_lookup_csums_bitmap(csum_root, stripe->logical,
                                                stripe_end, stripe->csums,
                                                &csum_bitmap, true);
                if (ret < 0)
                        goto out;
                if (ret > 0)
                        ret = 0;

                for_each_set_bit(sector_nr, &csum_bitmap, stripe->nr_sectors) {
                        stripe->sectors[sector_nr].csum = stripe->csums +
                                sector_nr * fs_info->csum_size;
                }
        }
        set_bit(SCRUB_STRIPE_FLAG_INITIALIZED, &stripe->state);
out:
        btrfs_release_path(&path);
        return ret;
}

static void scrub_reset_stripe(struct scrub_stripe *stripe)
{
        scrub_stripe_reset_bitmaps(stripe);

        stripe->nr_meta_extents = 0;
        stripe->nr_data_extents = 0;
        stripe->state = 0;

        for (int i = 0; i < stripe->nr_sectors; i++) {
                stripe->sectors[i].is_metadata = false;
                stripe->sectors[i].csum = NULL;
                stripe->sectors[i].generation = 0;
        }
}

static void scrub_submit_initial_read(struct scrub_ctx *sctx,
                                      struct scrub_stripe *stripe)
{
        struct btrfs_fs_info *fs_info = sctx->fs_info;
        struct btrfs_bio *bbio;
        int mirror = stripe->mirror_num;

        ASSERT(stripe->bg);
        ASSERT(stripe->mirror_num > 0);
        ASSERT(test_bit(SCRUB_STRIPE_FLAG_INITIALIZED, &stripe->state));

        bbio = btrfs_bio_alloc(SCRUB_STRIPE_PAGES, REQ_OP_READ, fs_info,
                               scrub_read_endio, stripe);

        /* Read the whole stripe. */
        bbio->bio.bi_iter.bi_sector = stripe->logical >> SECTOR_SHIFT;
        for (int i = 0; i < BTRFS_STRIPE_LEN >> PAGE_SHIFT; i++) {
                int ret;

                ret = bio_add_page(&bbio->bio, stripe->pages[i], PAGE_SIZE, 0);
                /* We should have allocated enough bio vectors. */
                ASSERT(ret == PAGE_SIZE);
        }
        atomic_inc(&stripe->pending_io);

        /*
         * For dev-replace, either user asks to avoid the source dev, or
         * the device is missing, we try the next mirror instead.
         */
        if (sctx->is_dev_replace &&
            (fs_info->dev_replace.cont_reading_from_srcdev_mode ==
             BTRFS_DEV_REPLACE_ITEM_CONT_READING_FROM_SRCDEV_MODE_AVOID ||
             !stripe->dev->bdev)) {
                int num_copies = btrfs_num_copies(fs_info, stripe->bg->start,
                                                  stripe->bg->length);

                mirror = calc_next_mirror(mirror, num_copies);
        }
        btrfs_submit_bio(bbio, mirror);
}

static bool stripe_has_metadata_error(struct scrub_stripe *stripe)
{
        int i;

        for_each_set_bit(i, &stripe->error_bitmap, stripe->nr_sectors) {
                if (stripe->sectors[i].is_metadata) {
                        struct btrfs_fs_info *fs_info = stripe->bg->fs_info;

                        btrfs_err(fs_info,
                        "stripe %llu has unrepaired metadata sector at %llu",
                                  stripe->logical,
                                  stripe->logical + (i << fs_info->sectorsize_bits));
                        return true;
                }
        }
        return false;
}

static int flush_scrub_stripes(struct scrub_ctx *sctx)
{
        struct btrfs_fs_info *fs_info = sctx->fs_info;
        struct scrub_stripe *stripe;
        const int nr_stripes = sctx->cur_stripe;
        int ret = 0;

        if (!nr_stripes)
                return 0;

        ASSERT(test_bit(SCRUB_STRIPE_FLAG_INITIALIZED, &sctx->stripes[0].state));

        scrub_throttle_dev_io(sctx, sctx->stripes[0].dev,
                              nr_stripes << BTRFS_STRIPE_LEN_SHIFT);
        for (int i = 0; i < nr_stripes; i++) {
                stripe = &sctx->stripes[i];
                scrub_submit_initial_read(sctx, stripe);
        }

        for (int i = 0; i < nr_stripes; i++) {
                stripe = &sctx->stripes[i];

                wait_event(stripe->repair_wait,
                           test_bit(SCRUB_STRIPE_FLAG_REPAIR_DONE, &stripe->state));
        }

        /*
         * Submit the repaired sectors.  For zoned case, we cannot do repair
         * in-place, but queue the bg to be relocated.
         */
        if (btrfs_is_zoned(fs_info)) {
                for (int i = 0; i < nr_stripes; i++) {
                        stripe = &sctx->stripes[i];

                        if (!bitmap_empty(&stripe->error_bitmap, stripe->nr_sectors)) {
                                btrfs_repair_one_zone(fs_info,
                                                      sctx->stripes[0].bg->start);
                                break;
                        }
                }
        } else {
                for (int i = 0; i < nr_stripes; i++) {
                        unsigned long repaired;

                        stripe = &sctx->stripes[i];

                        bitmap_andnot(&repaired, &stripe->init_error_bitmap,
                                      &stripe->error_bitmap, stripe->nr_sectors);
                        scrub_write_sectors(sctx, stripe, repaired, false);
                }
        }

        /* Submit for dev-replace. */
        if (sctx->is_dev_replace) {
                /*
                 * For dev-replace, if we know there is something wrong with
                 * metadata, we should immedately abort.
                 */
                for (int i = 0; i < nr_stripes; i++) {
                        if (stripe_has_metadata_error(&sctx->stripes[i])) {
                                ret = -EIO;
                                goto out;
                        }
                }
                for (int i = 0; i < nr_stripes; i++) {
                        unsigned long good;

                        stripe = &sctx->stripes[i];

                        ASSERT(stripe->dev == fs_info->dev_replace.srcdev);

                        bitmap_andnot(&good, &stripe->extent_sector_bitmap,
                                      &stripe->error_bitmap, stripe->nr_sectors);
                        scrub_write_sectors(sctx, stripe, good, true);
                }
        }

        /* Wait for the above writebacks to finish. */
        for (int i = 0; i < nr_stripes; i++) {
                stripe = &sctx->stripes[i];

                wait_scrub_stripe_io(stripe);
                scrub_reset_stripe(stripe);
        }
out:
        sctx->cur_stripe = 0;
        return ret;
}

static void raid56_scrub_wait_endio(struct bio *bio)
{
        complete(bio->bi_private);
}

static int queue_scrub_stripe(struct scrub_ctx *sctx, struct btrfs_block_group *bg,
                              struct btrfs_device *dev, int mirror_num,
                              u64 logical, u32 length, u64 physical)
{
        struct scrub_stripe *stripe;
        int ret;

        /* No available slot, submit all stripes and wait for them. */
        if (sctx->cur_stripe >= SCRUB_STRIPES_PER_SCTX) {
                ret = flush_scrub_stripes(sctx);
                if (ret < 0)
                        return ret;
        }

        stripe = &sctx->stripes[sctx->cur_stripe];

        /* We can queue one stripe using the remaining slot. */
        scrub_reset_stripe(stripe);
        ret = scrub_find_fill_first_stripe(bg, dev, physical, mirror_num,
                                           logical, length, stripe);
        /* Either >0 as no more extents or <0 for error. */
        if (ret)
                return ret;
        sctx->cur_stripe++;
        return 0;
}

static int scrub_raid56_parity_stripe(struct scrub_ctx *sctx,
                                      struct btrfs_device *scrub_dev,
                                      struct btrfs_block_group *bg,
                                      struct map_lookup *map,
                                      u64 full_stripe_start)
{
        DECLARE_COMPLETION_ONSTACK(io_done);
        struct btrfs_fs_info *fs_info = sctx->fs_info;
        struct btrfs_raid_bio *rbio;
        struct btrfs_io_context *bioc = NULL;
        struct bio *bio;
        struct scrub_stripe *stripe;
        bool all_empty = true;
        const int data_stripes = nr_data_stripes(map);
        unsigned long extent_bitmap = 0;
        u64 length = data_stripes << BTRFS_STRIPE_LEN_SHIFT;
        int ret;

        ASSERT(sctx->raid56_data_stripes);

        for (int i = 0; i < data_stripes; i++) {
                int stripe_index;
                int rot;
                u64 physical;

                stripe = &sctx->raid56_data_stripes[i];
                rot = div_u64(full_stripe_start - bg->start,
                              data_stripes) >> BTRFS_STRIPE_LEN_SHIFT;
                stripe_index = (i + rot) % map->num_stripes;
                physical = map->stripes[stripe_index].physical +
                           (rot << BTRFS_STRIPE_LEN_SHIFT);

                scrub_reset_stripe(stripe);
                set_bit(SCRUB_STRIPE_FLAG_NO_REPORT, &stripe->state);
                ret = scrub_find_fill_first_stripe(bg,
                                map->stripes[stripe_index].dev, physical, 1,
                                full_stripe_start + (i << BTRFS_STRIPE_LEN_SHIFT),
                                BTRFS_STRIPE_LEN, stripe);
                if (ret < 0)
                        goto out;
                /*
                 * No extent in this data stripe, need to manually mark them
                 * initialized to make later read submission happy.
                 */
                if (ret > 0) {
                        stripe->logical = full_stripe_start +
                                          (i << BTRFS_STRIPE_LEN_SHIFT);
                        stripe->dev = map->stripes[stripe_index].dev;
                        stripe->mirror_num = 1;
                        set_bit(SCRUB_STRIPE_FLAG_INITIALIZED, &stripe->state);
                }
        }

        /* Check if all data stripes are empty. */
        for (int i = 0; i < data_stripes; i++) {
                stripe = &sctx->raid56_data_stripes[i];
                if (!bitmap_empty(&stripe->extent_sector_bitmap, stripe->nr_sectors)) {
                        all_empty = false;
                        break;
                }
        }
        if (all_empty) {
                ret = 0;
                goto out;
        }

        for (int i = 0; i < data_stripes; i++) {
                stripe = &sctx->raid56_data_stripes[i];
                scrub_submit_initial_read(sctx, stripe);
        }
        for (int i = 0; i < data_stripes; i++) {
                stripe = &sctx->raid56_data_stripes[i];

                wait_event(stripe->repair_wait,
                           test_bit(SCRUB_STRIPE_FLAG_REPAIR_DONE, &stripe->state));
        }
        /* For now, no zoned support for RAID56. */
        ASSERT(!btrfs_is_zoned(sctx->fs_info));

        /* Writeback for the repaired sectors. */
        for (int i = 0; i < data_stripes; i++) {
                unsigned long repaired;

                stripe = &sctx->raid56_data_stripes[i];

                bitmap_andnot(&repaired, &stripe->init_error_bitmap,
                              &stripe->error_bitmap, stripe->nr_sectors);
                scrub_write_sectors(sctx, stripe, repaired, false);
        }

        /* Wait for the above writebacks to finish. */
        for (int i = 0; i < data_stripes; i++) {
                stripe = &sctx->raid56_data_stripes[i];

                wait_scrub_stripe_io(stripe);
        }

        /*
         * Now all data stripes are properly verified. Check if we have any
         * unrepaired, if so abort immediately or we could further corrupt the
         * P/Q stripes.
         *
         * During the loop, also populate extent_bitmap.
         */
        for (int i = 0; i < data_stripes; i++) {
                unsigned long error;

                stripe = &sctx->raid56_data_stripes[i];

                /*
                 * We should only check the errors where there is an extent.
                 * As we may hit an empty data stripe while it's missing.
                 */
                bitmap_and(&error, &stripe->error_bitmap,
                           &stripe->extent_sector_bitmap, stripe->nr_sectors);
                if (!bitmap_empty(&error, stripe->nr_sectors)) {
                        btrfs_err(fs_info,
"unrepaired sectors detected, full stripe %llu data stripe %u errors %*pbl",
                                  full_stripe_start, i, stripe->nr_sectors,
                                  &error);
                        ret = -EIO;
                        goto out;
                }
                bitmap_or(&extent_bitmap, &extent_bitmap,
                          &stripe->extent_sector_bitmap, stripe->nr_sectors);
        }

        /* Now we can check and regenerate the P/Q stripe. */
        bio = bio_alloc(NULL, 1, REQ_OP_READ, GFP_NOFS);
        bio->bi_iter.bi_sector = full_stripe_start >> SECTOR_SHIFT;
        bio->bi_private = &io_done;
        bio->bi_end_io = raid56_scrub_wait_endio;

        btrfs_bio_counter_inc_blocked(fs_info);
        ret = btrfs_map_sblock(fs_info, BTRFS_MAP_WRITE, full_stripe_start,
                               &length, &bioc);
        if (ret < 0) {
                btrfs_put_bioc(bioc);
                btrfs_bio_counter_dec(fs_info);
                goto out;
        }
        rbio = raid56_parity_alloc_scrub_rbio(bio, bioc, scrub_dev, &extent_bitmap,
                                BTRFS_STRIPE_LEN >> fs_info->sectorsize_bits);
        btrfs_put_bioc(bioc);
        if (!rbio) {
                ret = -ENOMEM;
                btrfs_bio_counter_dec(fs_info);
                goto out;
        }
        raid56_parity_submit_scrub_rbio(rbio);
        wait_for_completion_io(&io_done);
        ret = blk_status_to_errno(bio->bi_status);
        bio_put(bio);
        btrfs_bio_counter_dec(fs_info);

out:
        return ret;
}

/*
 * Scrub one range which can only has simple mirror based profile.
 * (Including all range in SINGLE/DUP/RAID1/RAID1C*, and each stripe in
 *  RAID0/RAID10).
 *
 * Since we may need to handle a subset of block group, we need @logical_start
 * and @logical_length parameter.
 */
static int scrub_simple_mirror(struct scrub_ctx *sctx,
                               struct btrfs_block_group *bg,
                               struct map_lookup *map,
                               u64 logical_start, u64 logical_length,
                               struct btrfs_device *device,
                               u64 physical, int mirror_num)
{
        struct btrfs_fs_info *fs_info = sctx->fs_info;
        const u64 logical_end = logical_start + logical_length;
        /* An artificial limit, inherit from old scrub behavior */
        struct btrfs_path path = { 0 };
        u64 cur_logical = logical_start;
        int ret;

        /* The range must be inside the bg */
        ASSERT(logical_start >= bg->start && logical_end <= bg->start + bg->length);

        path.search_commit_root = 1;
        path.skip_locking = 1;
        /* Go through each extent items inside the logical range */
        while (cur_logical < logical_end) {
                u64 cur_physical = physical + cur_logical - logical_start;

                /* Canceled? */
                if (atomic_read(&fs_info->scrub_cancel_req) ||
                    atomic_read(&sctx->cancel_req)) {
                        ret = -ECANCELED;
                        break;
                }
                /* Paused? */
                if (atomic_read(&fs_info->scrub_pause_req)) {
                        /* Push queued extents */
                        scrub_blocked_if_needed(fs_info);
                }
                /* Block group removed? */
                spin_lock(&bg->lock);
                if (test_bit(BLOCK_GROUP_FLAG_REMOVED, &bg->runtime_flags)) {
                        spin_unlock(&bg->lock);
                        ret = 0;
                        break;
                }
                spin_unlock(&bg->lock);

                ret = queue_scrub_stripe(sctx, bg, device, mirror_num,
                                         cur_logical, logical_end - cur_logical,
                                         cur_physical);
                if (ret > 0) {
                        /* No more extent, just update the accounting */
                        sctx->stat.last_physical = physical + logical_length;
                        ret = 0;
                        break;
                }
                if (ret < 0)
                        break;

                ASSERT(sctx->cur_stripe > 0);
                cur_logical = sctx->stripes[sctx->cur_stripe - 1].logical
                              + BTRFS_STRIPE_LEN;

                /* Don't hold CPU for too long time */
                cond_resched();
        }
        btrfs_release_path(&path);
        return ret;
}

/* Calculate the full stripe length for simple stripe based profiles */
static u64 simple_stripe_full_stripe_len(const struct map_lookup *map)
{
        ASSERT(map->type & (BTRFS_BLOCK_GROUP_RAID0 |
                            BTRFS_BLOCK_GROUP_RAID10));

        return (map->num_stripes / map->sub_stripes) << BTRFS_STRIPE_LEN_SHIFT;
}

/* Get the logical bytenr for the stripe */
static u64 simple_stripe_get_logical(struct map_lookup *map,
                                     struct btrfs_block_group *bg,
                                     int stripe_index)
{
        ASSERT(map->type & (BTRFS_BLOCK_GROUP_RAID0 |
                            BTRFS_BLOCK_GROUP_RAID10));
        ASSERT(stripe_index < map->num_stripes);

        /*
         * (stripe_index / sub_stripes) gives how many data stripes we need to
         * skip.
         */
        return ((stripe_index / map->sub_stripes) << BTRFS_STRIPE_LEN_SHIFT) +
               bg->start;
}

/* Get the mirror number for the stripe */
static int simple_stripe_mirror_num(struct map_lookup *map, int stripe_index)
{
        ASSERT(map->type & (BTRFS_BLOCK_GROUP_RAID0 |
                            BTRFS_BLOCK_GROUP_RAID10));
        ASSERT(stripe_index < map->num_stripes);

        /* For RAID0, it's fixed to 1, for RAID10 it's 0,1,0,1... */
        return stripe_index % map->sub_stripes + 1;
}

static int scrub_simple_stripe(struct scrub_ctx *sctx,
                               struct btrfs_block_group *bg,
                               struct map_lookup *map,
                               struct btrfs_device *device,
                               int stripe_index)
{
        const u64 logical_increment = simple_stripe_full_stripe_len(map);
        const u64 orig_logical = simple_stripe_get_logical(map, bg, stripe_index);
        const u64 orig_physical = map->stripes[stripe_index].physical;
        const int mirror_num = simple_stripe_mirror_num(map, stripe_index);
        u64 cur_logical = orig_logical;
        u64 cur_physical = orig_physical;
        int ret = 0;

        while (cur_logical < bg->start + bg->length) {
                /*
                 * Inside each stripe, RAID0 is just SINGLE, and RAID10 is
                 * just RAID1, so we can reuse scrub_simple_mirror() to scrub
                 * this stripe.
                 */
                ret = scrub_simple_mirror(sctx, bg, map, cur_logical,
                                          BTRFS_STRIPE_LEN, device, cur_physical,
                                          mirror_num);
                if (ret)
                        return ret;
                /* Skip to next stripe which belongs to the target device */
                cur_logical += logical_increment;
                /* For physical offset, we just go to next stripe */
                cur_physical += BTRFS_STRIPE_LEN;
        }
        return ret;
}

static noinline_for_stack int scrub_stripe(struct scrub_ctx *sctx,
                                           struct btrfs_block_group *bg,
                                           struct extent_map *em,
                                           struct btrfs_device *scrub_dev,
                                           int stripe_index)
{
        struct btrfs_fs_info *fs_info = sctx->fs_info;
        struct map_lookup *map = em->map_lookup;
        const u64 profile = map->type & BTRFS_BLOCK_GROUP_PROFILE_MASK;
        const u64 chunk_logical = bg->start;
        int ret;
        int ret2;
        u64 physical = map->stripes[stripe_index].physical;
        const u64 dev_stripe_len = btrfs_calc_stripe_length(em);
        const u64 physical_end = physical + dev_stripe_len;
        u64 logical;
        u64 logic_end;
        /* The logical increment after finishing one stripe */
        u64 increment;
        /* Offset inside the chunk */
        u64 offset;
        u64 stripe_logical;
        int stop_loop = 0;

        scrub_blocked_if_needed(fs_info);

        if (sctx->is_dev_replace &&
            btrfs_dev_is_sequential(sctx->wr_tgtdev, physical)) {
                mutex_lock(&sctx->wr_lock);
                sctx->write_pointer = physical;
                mutex_unlock(&sctx->wr_lock);
        }

        /* Prepare the extra data stripes used by RAID56. */
        if (profile & BTRFS_BLOCK_GROUP_RAID56_MASK) {
                ASSERT(sctx->raid56_data_stripes == NULL);

                sctx->raid56_data_stripes = kcalloc(nr_data_stripes(map),
                                                    sizeof(struct scrub_stripe),
                                                    GFP_KERNEL);
                if (!sctx->raid56_data_stripes) {
                        ret = -ENOMEM;
                        goto out;
                }
                for (int i = 0; i < nr_data_stripes(map); i++) {
                        ret = init_scrub_stripe(fs_info,
                                                &sctx->raid56_data_stripes[i]);
                        if (ret < 0)
                                goto out;
                        sctx->raid56_data_stripes[i].bg = bg;
                        sctx->raid56_data_stripes[i].sctx = sctx;
                }
        }
        /*
         * There used to be a big double loop to handle all profiles using the
         * same routine, which grows larger and more gross over time.
         *
         * So here we handle each profile differently, so simpler profiles
         * have simpler scrubbing function.
         */
        if (!(profile & (BTRFS_BLOCK_GROUP_RAID0 | BTRFS_BLOCK_GROUP_RAID10 |
                         BTRFS_BLOCK_GROUP_RAID56_MASK))) {
                /*
                 * Above check rules out all complex profile, the remaining
                 * profiles are SINGLE|DUP|RAID1|RAID1C*, which is simple
                 * mirrored duplication without stripe.
                 *
                 * Only @physical and @mirror_num needs to calculated using
                 * @stripe_index.
                 */
                ret = scrub_simple_mirror(sctx, bg, map, bg->start, bg->length,
                                scrub_dev, map->stripes[stripe_index].physical,
                                stripe_index + 1);
                offset = 0;
                goto out;
        }
        if (profile & (BTRFS_BLOCK_GROUP_RAID0 | BTRFS_BLOCK_GROUP_RAID10)) {
                ret = scrub_simple_stripe(sctx, bg, map, scrub_dev, stripe_index);
                offset = (stripe_index / map->sub_stripes) << BTRFS_STRIPE_LEN_SHIFT;
                goto out;
        }

        /* Only RAID56 goes through the old code */
        ASSERT(map->type & BTRFS_BLOCK_GROUP_RAID56_MASK);
        ret = 0;

        /* Calculate the logical end of the stripe */
        get_raid56_logic_offset(physical_end, stripe_index,
                                map, &logic_end, NULL);
        logic_end += chunk_logical;

        /* Initialize @offset in case we need to go to out: label */
        get_raid56_logic_offset(physical, stripe_index, map, &offset, NULL);
        increment = nr_data_stripes(map) << BTRFS_STRIPE_LEN_SHIFT;

        /*
         * Due to the rotation, for RAID56 it's better to iterate each stripe
         * using their physical offset.
         */
        while (physical < physical_end) {
                ret = get_raid56_logic_offset(physical, stripe_index, map,
                                              &logical, &stripe_logical);
                logical += chunk_logical;
                if (ret) {
                        /* it is parity strip */
                        stripe_logical += chunk_logical;
                        ret = scrub_raid56_parity_stripe(sctx, scrub_dev, bg,
                                                         map, stripe_logical);
                        if (ret)
                                goto out;
                        goto next;
                }

                /*
                 * Now we're at a data stripe, scrub each extents in the range.
                 *
                 * At this stage, if we ignore the repair part, inside each data
                 * stripe it is no different than SINGLE profile.
                 * We can reuse scrub_simple_mirror() here, as the repair part
                 * is still based on @mirror_num.
                 */
                ret = scrub_simple_mirror(sctx, bg, map, logical, BTRFS_STRIPE_LEN,
                                          scrub_dev, physical, 1);
                if (ret < 0)
                        goto out;
next:
                logical += increment;
                physical += BTRFS_STRIPE_LEN;
                spin_lock(&sctx->stat_lock);
                if (stop_loop)
                        sctx->stat.last_physical =
                                map->stripes[stripe_index].physical + dev_stripe_len;
                else
                        sctx->stat.last_physical = physical;
                spin_unlock(&sctx->stat_lock);
                if (stop_loop)
                        break;
        }
out:
        ret2 = flush_scrub_stripes(sctx);
        if (!ret2)
                ret = ret2;
        if (sctx->raid56_data_stripes) {
                for (int i = 0; i < nr_data_stripes(map); i++)
                        release_scrub_stripe(&sctx->raid56_data_stripes[i]);
                kfree(sctx->raid56_data_stripes);
                sctx->raid56_data_stripes = NULL;
        }

        if (sctx->is_dev_replace && ret >= 0) {
                int ret2;

                ret2 = sync_write_pointer_for_zoned(sctx,
                                chunk_logical + offset,
                                map->stripes[stripe_index].physical,
                                physical_end);
                if (ret2)
                        ret = ret2;
        }

        return ret < 0 ? ret : 0;
}

static noinline_for_stack int scrub_chunk(struct scrub_ctx *sctx,
                                          struct btrfs_block_group *bg,
                                          struct btrfs_device *scrub_dev,
                                          u64 dev_offset,
                                          u64 dev_extent_len)
{
        struct btrfs_fs_info *fs_info = sctx->fs_info;
        struct extent_map_tree *map_tree = &fs_info->mapping_tree;
        struct map_lookup *map;
        struct extent_map *em;
        int i;
        int ret = 0;

        read_lock(&map_tree->lock);
        em = lookup_extent_mapping(map_tree, bg->start, bg->length);
        read_unlock(&map_tree->lock);

        if (!em) {
                /*
                 * Might have been an unused block group deleted by the cleaner
                 * kthread or relocation.
                 */
                spin_lock(&bg->lock);
                if (!test_bit(BLOCK_GROUP_FLAG_REMOVED, &bg->runtime_flags))
                        ret = -EINVAL;
                spin_unlock(&bg->lock);

                return ret;
        }
        if (em->start != bg->start)
                goto out;
        if (em->len < dev_extent_len)
                goto out;

        map = em->map_lookup;
        for (i = 0; i < map->num_stripes; ++i) {
                if (map->stripes[i].dev->bdev == scrub_dev->bdev &&
                    map->stripes[i].physical == dev_offset) {
                        ret = scrub_stripe(sctx, bg, em, scrub_dev, i);
                        if (ret)
                                goto out;
                }
        }
out:
        free_extent_map(em);

        return ret;
}

static int finish_extent_writes_for_zoned(struct btrfs_root *root,
                                          struct btrfs_block_group *cache)
{
        struct btrfs_fs_info *fs_info = cache->fs_info;
        struct btrfs_trans_handle *trans;

        if (!btrfs_is_zoned(fs_info))
                return 0;

        btrfs_wait_block_group_reservations(cache);
        btrfs_wait_nocow_writers(cache);
        btrfs_wait_ordered_roots(fs_info, U64_MAX, cache->start, cache->length);

        trans = btrfs_join_transaction(root);
        if (IS_ERR(trans))
                return PTR_ERR(trans);
        return btrfs_commit_transaction(trans);
}

static noinline_for_stack
int scrub_enumerate_chunks(struct scrub_ctx *sctx,
                           struct btrfs_device *scrub_dev, u64 start, u64 end)
{
        struct btrfs_dev_extent *dev_extent = NULL;
        struct btrfs_path *path;
        struct btrfs_fs_info *fs_info = sctx->fs_info;
        struct btrfs_root *root = fs_info->dev_root;
        u64 chunk_offset;
        int ret = 0;
        int ro_set;
        int slot;
        struct extent_buffer *l;
        struct btrfs_key key;
        struct btrfs_key found_key;
        struct btrfs_block_group *cache;
        struct btrfs_dev_replace *dev_replace = &fs_info->dev_replace;

        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;

        path->reada = READA_FORWARD;
        path->search_commit_root = 1;
        path->skip_locking = 1;

        key.objectid = scrub_dev->devid;
        key.offset = 0ull;
        key.type = BTRFS_DEV_EXTENT_KEY;

        while (1) {
                u64 dev_extent_len;

                ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
                if (ret < 0)
                        break;
                if (ret > 0) {
                        if (path->slots[0] >=
                            btrfs_header_nritems(path->nodes[0])) {
                                ret = btrfs_next_leaf(root, path);
                                if (ret < 0)
                                        break;
                                if (ret > 0) {
                                        ret = 0;
                                        break;
                                }
                        } else {
                                ret = 0;
                        }
                }

                l = path->nodes[0];
                slot = path->slots[0];

                btrfs_item_key_to_cpu(l, &found_key, slot);

                if (found_key.objectid != scrub_dev->devid)
                        break;

                if (found_key.type != BTRFS_DEV_EXTENT_KEY)
                        break;

                if (found_key.offset >= end)
                        break;

                if (found_key.offset < key.offset)
                        break;

                dev_extent = btrfs_item_ptr(l, slot, struct btrfs_dev_extent);
                dev_extent_len = btrfs_dev_extent_length(l, dev_extent);

                if (found_key.offset + dev_extent_len <= start)
                        goto skip;

                chunk_offset = btrfs_dev_extent_chunk_offset(l, dev_extent);

                /*
                 * get a reference on the corresponding block group to prevent
                 * the chunk from going away while we scrub it
                 */
                cache = btrfs_lookup_block_group(fs_info, chunk_offset);

                /* some chunks are removed but not committed to disk yet,
                 * continue scrubbing */
                if (!cache)
                        goto skip;

                ASSERT(cache->start <= chunk_offset);
                /*
                 * We are using the commit root to search for device extents, so
                 * that means we could have found a device extent item from a
                 * block group that was deleted in the current transaction. The
                 * logical start offset of the deleted block group, stored at
                 * @chunk_offset, might be part of the logical address range of
                 * a new block group (which uses different physical extents).
                 * In this case btrfs_lookup_block_group() has returned the new
                 * block group, and its start address is less than @chunk_offset.
                 *
                 * We skip such new block groups, because it's pointless to
                 * process them, as we won't find their extents because we search
                 * for them using the commit root of the extent tree. For a device
                 * replace it's also fine to skip it, we won't miss copying them
                 * to the target device because we have the write duplication
                 * setup through the regular write path (by btrfs_map_block()),
                 * and we have committed a transaction when we started the device
                 * replace, right after setting up the device replace state.
                 */
                if (cache->start < chunk_offset) {
                        btrfs_put_block_group(cache);
                        goto skip;
                }

                if (sctx->is_dev_replace && btrfs_is_zoned(fs_info)) {
                        if (!test_bit(BLOCK_GROUP_FLAG_TO_COPY, &cache->runtime_flags)) {
                                btrfs_put_block_group(cache);
                                goto skip;
                        }
                }

                /*
                 * Make sure that while we are scrubbing the corresponding block
                 * group doesn't get its logical address and its device extents
                 * reused for another block group, which can possibly be of a
                 * different type and different profile. We do this to prevent
                 * false error detections and crashes due to bogus attempts to
                 * repair extents.
                 */
                spin_lock(&cache->lock);
                if (test_bit(BLOCK_GROUP_FLAG_REMOVED, &cache->runtime_flags)) {
                        spin_unlock(&cache->lock);
                        btrfs_put_block_group(cache);
                        goto skip;
                }
                btrfs_freeze_block_group(cache);
                spin_unlock(&cache->lock);

                /*
                 * we need call btrfs_inc_block_group_ro() with scrubs_paused,
                 * to avoid deadlock caused by:
                 * btrfs_inc_block_group_ro()
                 * -> btrfs_wait_for_commit()
                 * -> btrfs_commit_transaction()
                 * -> btrfs_scrub_pause()
                 */
                scrub_pause_on(fs_info);

                /*
                 * Don't do chunk preallocation for scrub.
                 *
                 * This is especially important for SYSTEM bgs, or we can hit
                 * -EFBIG from btrfs_finish_chunk_alloc() like:
                 * 1. The only SYSTEM bg is marked RO.
                 *    Since SYSTEM bg is small, that's pretty common.
                 * 2. New SYSTEM bg will be allocated
                 *    Due to regular version will allocate new chunk.
                 * 3. New SYSTEM bg is empty and will get cleaned up
                 *    Before cleanup really happens, it's marked RO again.
                 * 4. Empty SYSTEM bg get scrubbed
                 *    We go back to 2.
                 *
                 * This can easily boost the amount of SYSTEM chunks if cleaner
                 * thread can't be triggered fast enough, and use up all space
                 * of btrfs_super_block::sys_chunk_array
                 *
                 * While for dev replace, we need to try our best to mark block
                 * group RO, to prevent race between:
                 * - Write duplication
                 *   Contains latest data
                 * - Scrub copy
                 *   Contains data from commit tree
                 *
                 * If target block group is not marked RO, nocow writes can
                 * be overwritten by scrub copy, causing data corruption.
                 * So for dev-replace, it's not allowed to continue if a block
                 * group is not RO.
                 */
                ret = btrfs_inc_block_group_ro(cache, sctx->is_dev_replace);
                if (!ret && sctx->is_dev_replace) {
                        ret = finish_extent_writes_for_zoned(root, cache);
                        if (ret) {
                                btrfs_dec_block_group_ro(cache);
                                scrub_pause_off(fs_info);
                                btrfs_put_block_group(cache);
                                break;
                        }
                }

                if (ret == 0) {
                        ro_set = 1;
                } else if (ret == -ENOSPC && !sctx->is_dev_replace) {
                        /*
                         * btrfs_inc_block_group_ro return -ENOSPC when it
                         * failed in creating new chunk for metadata.
                         * It is not a problem for scrub, because
                         * metadata are always cowed, and our scrub paused
                         * commit_transactions.
                         */
                        ro_set = 0;
                } else if (ret == -ETXTBSY) {
                        btrfs_warn(fs_info,
                   "skipping scrub of block group %llu due to active swapfile",
                                   cache->start);
                        scrub_pause_off(fs_info);
                        ret = 0;
                        goto skip_unfreeze;
                } else {
                        btrfs_warn(fs_info,
                                   "failed setting block group ro: %d", ret);
                        btrfs_unfreeze_block_group(cache);
                        btrfs_put_block_group(cache);
                        scrub_pause_off(fs_info);
                        break;
                }

                /*
                 * Now the target block is marked RO, wait for nocow writes to
                 * finish before dev-replace.
                 * COW is fine, as COW never overwrites extents in commit tree.
                 */
                if (sctx->is_dev_replace) {
                        btrfs_wait_nocow_writers(cache);
                        btrfs_wait_ordered_roots(fs_info, U64_MAX, cache->start,
                                        cache->length);
                }

                scrub_pause_off(fs_info);
                down_write(&dev_replace->rwsem);
                dev_replace->cursor_right = found_key.offset + dev_extent_len;
                dev_replace->cursor_left = found_key.offset;
                dev_replace->item_needs_writeback = 1;
                up_write(&dev_replace->rwsem);

                ret = scrub_chunk(sctx, cache, scrub_dev, found_key.offset,
                                  dev_extent_len);
                if (sctx->is_dev_replace &&
                    !btrfs_finish_block_group_to_copy(dev_replace->srcdev,
                                                      cache, found_key.offset))
                        ro_set = 0;

                down_write(&dev_replace->rwsem);
                dev_replace->cursor_left = dev_replace->cursor_right;
                dev_replace->item_needs_writeback = 1;
                up_write(&dev_replace->rwsem);

                if (ro_set)
                        btrfs_dec_block_group_ro(cache);

                /*
                 * We might have prevented the cleaner kthread from deleting
                 * this block group if it was already unused because we raced
                 * and set it to RO mode first. So add it back to the unused
                 * list, otherwise it might not ever be deleted unless a manual
                 * balance is triggered or it becomes used and unused again.
                 */
                spin_lock(&cache->lock);
                if (!test_bit(BLOCK_GROUP_FLAG_REMOVED, &cache->runtime_flags) &&
                    !cache->ro && cache->reserved == 0 && cache->used == 0) {
                        spin_unlock(&cache->lock);
                        if (btrfs_test_opt(fs_info, DISCARD_ASYNC))
                                btrfs_discard_queue_work(&fs_info->discard_ctl,
                                                         cache);
                        else
                                btrfs_mark_bg_unused(cache);
                } else {
                        spin_unlock(&cache->lock);
                }
skip_unfreeze:
                btrfs_unfreeze_block_group(cache);
                btrfs_put_block_group(cache);
                if (ret)
                        break;
                if (sctx->is_dev_replace &&
                    atomic64_read(&dev_replace->num_write_errors) > 0) {
                        ret = -EIO;
                        break;
                }
                if (sctx->stat.malloc_errors > 0) {
                        ret = -ENOMEM;
                        break;
                }
skip:
                key.offset = found_key.offset + dev_extent_len;
                btrfs_release_path(path);
        }

        btrfs_free_path(path);

        return ret;
}

static int scrub_one_super(struct scrub_ctx *sctx, struct btrfs_device *dev,
                           struct page *page, u64 physical, u64 generation)
{
        struct btrfs_fs_info *fs_info = sctx->fs_info;
        struct bio_vec bvec;
        struct bio bio;
        struct btrfs_super_block *sb = page_address(page);
        int ret;

        bio_init(&bio, dev->bdev, &bvec, 1, REQ_OP_READ);
        bio.bi_iter.bi_sector = physical >> SECTOR_SHIFT;
        __bio_add_page(&bio, page, BTRFS_SUPER_INFO_SIZE, 0);
        ret = submit_bio_wait(&bio);
        bio_uninit(&bio);

        if (ret < 0)
                return ret;
        ret = btrfs_check_super_csum(fs_info, sb);
        if (ret != 0) {
                btrfs_err_rl(fs_info,
                        "super block at physical %llu devid %llu has bad csum",
                        physical, dev->devid);
                return -EIO;
        }
        if (btrfs_super_generation(sb) != generation) {
                btrfs_err_rl(fs_info,
"super block at physical %llu devid %llu has bad generation %llu expect %llu",
                             physical, dev->devid,
                             btrfs_super_generation(sb), generation);
                return -EUCLEAN;
        }

        return btrfs_validate_super(fs_info, sb, -1);
}

static noinline_for_stack int scrub_supers(struct scrub_ctx *sctx,
                                           struct btrfs_device *scrub_dev)
{
        int     i;
        u64     bytenr;
        u64     gen;
        int ret = 0;
        struct page *page;
        struct btrfs_fs_info *fs_info = sctx->fs_info;

        if (BTRFS_FS_ERROR(fs_info))
                return -EROFS;

        page = alloc_page(GFP_KERNEL);
        if (!page) {
                spin_lock(&sctx->stat_lock);
                sctx->stat.malloc_errors++;
                spin_unlock(&sctx->stat_lock);
                return -ENOMEM;
        }

        /* Seed devices of a new filesystem has their own generation. */
        if (scrub_dev->fs_devices != fs_info->fs_devices)
                gen = scrub_dev->generation;
        else
                gen = fs_info->last_trans_committed;

        for (i = 0; i < BTRFS_SUPER_MIRROR_MAX; i++) {
                bytenr = btrfs_sb_offset(i);
                if (bytenr + BTRFS_SUPER_INFO_SIZE >
                    scrub_dev->commit_total_bytes)
                        break;
                if (!btrfs_check_super_location(scrub_dev, bytenr))
                        continue;

                ret = scrub_one_super(sctx, scrub_dev, page, bytenr, gen);
                if (ret) {
                        spin_lock(&sctx->stat_lock);
                        sctx->stat.super_errors++;
                        spin_unlock(&sctx->stat_lock);
                }
        }
        __free_page(page);
        return 0;
}

static void scrub_workers_put(struct btrfs_fs_info *fs_info)
{
        if (refcount_dec_and_mutex_lock(&fs_info->scrub_workers_refcnt,
                                        &fs_info->scrub_lock)) {
                struct workqueue_struct *scrub_workers = fs_info->scrub_workers;
                struct workqueue_struct *scrub_wr_comp =
                                                fs_info->scrub_wr_completion_workers;

                fs_info->scrub_workers = NULL;
                fs_info->scrub_wr_completion_workers = NULL;
                mutex_unlock(&fs_info->scrub_lock);

                if (scrub_workers)
                        destroy_workqueue(scrub_workers);
                if (scrub_wr_comp)
                        destroy_workqueue(scrub_wr_comp);
        }
}

/*
 * get a reference count on fs_info->scrub_workers. start worker if necessary
 */
static noinline_for_stack int scrub_workers_get(struct btrfs_fs_info *fs_info,
                                                int is_dev_replace)
{
        struct workqueue_struct *scrub_workers = NULL;
        struct workqueue_struct *scrub_wr_comp = NULL;
        unsigned int flags = WQ_FREEZABLE | WQ_UNBOUND;
        int max_active = fs_info->thread_pool_size;
        int ret = -ENOMEM;

        if (refcount_inc_not_zero(&fs_info->scrub_workers_refcnt))
                return 0;

        scrub_workers = alloc_workqueue("btrfs-scrub", flags,
                                        is_dev_replace ? 1 : max_active);
        if (!scrub_workers)
                goto fail_scrub_workers;

        scrub_wr_comp = alloc_workqueue("btrfs-scrubwrc", flags, max_active);
        if (!scrub_wr_comp)
                goto fail_scrub_wr_completion_workers;

        mutex_lock(&fs_info->scrub_lock);
        if (refcount_read(&fs_info->scrub_workers_refcnt) == 0) {
                ASSERT(fs_info->scrub_workers == NULL &&
                       fs_info->scrub_wr_completion_workers == NULL);
                fs_info->scrub_workers = scrub_workers;
                fs_info->scrub_wr_completion_workers = scrub_wr_comp;
                refcount_set(&fs_info->scrub_workers_refcnt, 1);
                mutex_unlock(&fs_info->scrub_lock);
                return 0;
        }
        /* Other thread raced in and created the workers for us */
        refcount_inc(&fs_info->scrub_workers_refcnt);
        mutex_unlock(&fs_info->scrub_lock);

        ret = 0;

        destroy_workqueue(scrub_wr_comp);
fail_scrub_wr_completion_workers:
        destroy_workqueue(scrub_workers);
fail_scrub_workers:
        return ret;
}

int btrfs_scrub_dev(struct btrfs_fs_info *fs_info, u64 devid, u64 start,
                    u64 end, struct btrfs_scrub_progress *progress,
                    int readonly, int is_dev_replace)
{
        struct btrfs_dev_lookup_args args = { .devid = devid };
        struct scrub_ctx *sctx;
        int ret;
        struct btrfs_device *dev;
        unsigned int nofs_flag;
        bool need_commit = false;

        if (btrfs_fs_closing(fs_info))
                return -EAGAIN;

        /* At mount time we have ensured nodesize is in the range of [4K, 64K]. */
        ASSERT(fs_info->nodesize <= BTRFS_STRIPE_LEN);

        /*
         * SCRUB_MAX_SECTORS_PER_BLOCK is calculated using the largest possible
         * value (max nodesize / min sectorsize), thus nodesize should always
         * be fine.
         */
        ASSERT(fs_info->nodesize <=
               SCRUB_MAX_SECTORS_PER_BLOCK << fs_info->sectorsize_bits);

        /* Allocate outside of device_list_mutex */
        sctx = scrub_setup_ctx(fs_info, is_dev_replace);
        if (IS_ERR(sctx))
                return PTR_ERR(sctx);

        ret = scrub_workers_get(fs_info, is_dev_replace);
        if (ret)
                goto out_free_ctx;

        mutex_lock(&fs_info->fs_devices->device_list_mutex);
        dev = btrfs_find_device(fs_info->fs_devices, &args);
        if (!dev || (test_bit(BTRFS_DEV_STATE_MISSING, &dev->dev_state) &&
                     !is_dev_replace)) {
                mutex_unlock(&fs_info->fs_devices->device_list_mutex);
                ret = -ENODEV;
                goto out;
        }

        if (!is_dev_replace && !readonly &&
            !test_bit(BTRFS_DEV_STATE_WRITEABLE, &dev->dev_state)) {
                mutex_unlock(&fs_info->fs_devices->device_list_mutex);
                btrfs_err_in_rcu(fs_info,
                        "scrub on devid %llu: filesystem on %s is not writable",
                                 devid, btrfs_dev_name(dev));
                ret = -EROFS;
                goto out;
        }

        mutex_lock(&fs_info->scrub_lock);
        if (!test_bit(BTRFS_DEV_STATE_IN_FS_METADATA, &dev->dev_state) ||
            test_bit(BTRFS_DEV_STATE_REPLACE_TGT, &dev->dev_state)) {
                mutex_unlock(&fs_info->scrub_lock);
                mutex_unlock(&fs_info->fs_devices->device_list_mutex);
                ret = -EIO;
                goto out;
        }

        down_read(&fs_info->dev_replace.rwsem);
        if (dev->scrub_ctx ||
            (!is_dev_replace &&
             btrfs_dev_replace_is_ongoing(&fs_info->dev_replace))) {
                up_read(&fs_info->dev_replace.rwsem);
                mutex_unlock(&fs_info->scrub_lock);
                mutex_unlock(&fs_info->fs_devices->device_list_mutex);
                ret = -EINPROGRESS;
                goto out;
        }
        up_read(&fs_info->dev_replace.rwsem);

        sctx->readonly = readonly;
        dev->scrub_ctx = sctx;
        mutex_unlock(&fs_info->fs_devices->device_list_mutex);

        /*
         * checking @scrub_pause_req here, we can avoid
         * race between committing transaction and scrubbing.
         */
        __scrub_blocked_if_needed(fs_info);
        atomic_inc(&fs_info->scrubs_running);
        mutex_unlock(&fs_info->scrub_lock);

        /*
         * In order to avoid deadlock with reclaim when there is a transaction
         * trying to pause scrub, make sure we use GFP_NOFS for all the
         * allocations done at btrfs_scrub_sectors() and scrub_sectors_for_parity()
         * invoked by our callees. The pausing request is done when the
         * transaction commit starts, and it blocks the transaction until scrub
         * is paused (done at specific points at scrub_stripe() or right above
         * before incrementing fs_info->scrubs_running).
         */
        nofs_flag = memalloc_nofs_save();
        if (!is_dev_replace) {
                u64 old_super_errors;

                spin_lock(&sctx->stat_lock);
                old_super_errors = sctx->stat.super_errors;
                spin_unlock(&sctx->stat_lock);

                btrfs_info(fs_info, "scrub: started on devid %llu", devid);
                /*
                 * by holding device list mutex, we can
                 * kick off writing super in log tree sync.
                 */
                mutex_lock(&fs_info->fs_devices->device_list_mutex);
                ret = scrub_supers(sctx, dev);
                mutex_unlock(&fs_info->fs_devices->device_list_mutex);

                spin_lock(&sctx->stat_lock);
                /*
                 * Super block errors found, but we can not commit transaction
                 * at current context, since btrfs_commit_transaction() needs
                 * to pause the current running scrub (hold by ourselves).
                 */
                if (sctx->stat.super_errors > old_super_errors && !sctx->readonly)
                        need_commit = true;
                spin_unlock(&sctx->stat_lock);
        }

        if (!ret)
                ret = scrub_enumerate_chunks(sctx, dev, start, end);
        memalloc_nofs_restore(nofs_flag);

        atomic_dec(&fs_info->scrubs_running);
        wake_up(&fs_info->scrub_pause_wait);

        if (progress)
                memcpy(progress, &sctx->stat, sizeof(*progress));

        if (!is_dev_replace)
                btrfs_info(fs_info, "scrub: %s on devid %llu with status: %d",
                        ret ? "not finished" : "finished", devid, ret);

        mutex_lock(&fs_info->scrub_lock);
        dev->scrub_ctx = NULL;
        mutex_unlock(&fs_info->scrub_lock);

        scrub_workers_put(fs_info);
        scrub_put_ctx(sctx);

        /*
         * We found some super block errors before, now try to force a
         * transaction commit, as scrub has finished.
         */
        if (need_commit) {
                struct btrfs_trans_handle *trans;

                trans = btrfs_start_transaction(fs_info->tree_root, 0);
                if (IS_ERR(trans)) {
                        ret = PTR_ERR(trans);
                        btrfs_err(fs_info,
        "scrub: failed to start transaction to fix super block errors: %d", ret);
                        return ret;
                }
                ret = btrfs_commit_transaction(trans);
                if (ret < 0)
                        btrfs_err(fs_info,
        "scrub: failed to commit transaction to fix super block errors: %d", ret);
        }
        return ret;
out:
        scrub_workers_put(fs_info);
out_free_ctx:
        scrub_free_ctx(sctx);

        return ret;
}

void btrfs_scrub_pause(struct btrfs_fs_info *fs_info)
{
        mutex_lock(&fs_info->scrub_lock);
        atomic_inc(&fs_info->scrub_pause_req);
        while (atomic_read(&fs_info->scrubs_paused) !=
               atomic_read(&fs_info->scrubs_running)) {
                mutex_unlock(&fs_info->scrub_lock);
                wait_event(fs_info->scrub_pause_wait,
                           atomic_read(&fs_info->scrubs_paused) ==
                           atomic_read(&fs_info->scrubs_running));
                mutex_lock(&fs_info->scrub_lock);
        }
        mutex_unlock(&fs_info->scrub_lock);
}

void btrfs_scrub_continue(struct btrfs_fs_info *fs_info)
{
        atomic_dec(&fs_info->scrub_pause_req);
        wake_up(&fs_info->scrub_pause_wait);
}

int btrfs_scrub_cancel(struct btrfs_fs_info *fs_info)
{
        mutex_lock(&fs_info->scrub_lock);
        if (!atomic_read(&fs_info->scrubs_running)) {
                mutex_unlock(&fs_info->scrub_lock);
                return -ENOTCONN;
        }

        atomic_inc(&fs_info->scrub_cancel_req);
        while (atomic_read(&fs_info->scrubs_running)) {
                mutex_unlock(&fs_info->scrub_lock);
                wait_event(fs_info->scrub_pause_wait,
                           atomic_read(&fs_info->scrubs_running) == 0);
                mutex_lock(&fs_info->scrub_lock);
        }
        atomic_dec(&fs_info->scrub_cancel_req);
        mutex_unlock(&fs_info->scrub_lock);

        return 0;
}

int btrfs_scrub_cancel_dev(struct btrfs_device *dev)
{
        struct btrfs_fs_info *fs_info = dev->fs_info;
        struct scrub_ctx *sctx;

        mutex_lock(&fs_info->scrub_lock);
        sctx = dev->scrub_ctx;
        if (!sctx) {
                mutex_unlock(&fs_info->scrub_lock);
                return -ENOTCONN;
        }
        atomic_inc(&sctx->cancel_req);
        while (dev->scrub_ctx) {
                mutex_unlock(&fs_info->scrub_lock);
                wait_event(fs_info->scrub_pause_wait,
                           dev->scrub_ctx == NULL);
                mutex_lock(&fs_info->scrub_lock);
        }
        mutex_unlock(&fs_info->scrub_lock);

        return 0;
}

int btrfs_scrub_progress(struct btrfs_fs_info *fs_info, u64 devid,
                         struct btrfs_scrub_progress *progress)
{
        struct btrfs_dev_lookup_args args = { .devid = devid };
        struct btrfs_device *dev;
        struct scrub_ctx *sctx = NULL;

        mutex_lock(&fs_info->fs_devices->device_list_mutex);
        dev = btrfs_find_device(fs_info->fs_devices, &args);
        if (dev)
                sctx = dev->scrub_ctx;
        if (sctx)
                memcpy(progress, &sctx->stat, sizeof(*progress));
        mutex_unlock(&fs_info->fs_devices->device_list_mutex);

        return dev ? (sctx ? 0 : -ENOTCONN) : -ENODEV;
}