KVM: arm64: Add support for userspace to suspend a vCPU

[linux.git] / fs / xfs / libxfs / xfs_defer.c

// SPDX-License-Identifier: GPL-2.0+
/*
 * Copyright (C) 2016 Oracle.  All Rights Reserved.
 * Author: Darrick J. Wong <[email protected]>
 */
#include "xfs.h"
#include "xfs_fs.h"
#include "xfs_shared.h"
#include "xfs_format.h"
#include "xfs_log_format.h"
#include "xfs_trans_resv.h"
#include "xfs_mount.h"
#include "xfs_defer.h"
#include "xfs_trans.h"
#include "xfs_buf_item.h"
#include "xfs_inode.h"
#include "xfs_inode_item.h"
#include "xfs_trace.h"
#include "xfs_icache.h"
#include "xfs_log.h"
#include "xfs_rmap.h"
#include "xfs_refcount.h"
#include "xfs_bmap.h"
#include "xfs_alloc.h"

static struct kmem_cache        *xfs_defer_pending_cache;

/*
 * Deferred Operations in XFS
 *
 * Due to the way locking rules work in XFS, certain transactions (block
 * mapping and unmapping, typically) have permanent reservations so that
 * we can roll the transaction to adhere to AG locking order rules and
 * to unlock buffers between metadata updates.  Prior to rmap/reflink,
 * the mapping code had a mechanism to perform these deferrals for
 * extents that were going to be freed; this code makes that facility
 * more generic.
 *
 * When adding the reverse mapping and reflink features, it became
 * necessary to perform complex remapping multi-transactions to comply
 * with AG locking order rules, and to be able to spread a single
 * refcount update operation (an operation on an n-block extent can
 * update as many as n records!) among multiple transactions.  XFS can
 * roll a transaction to facilitate this, but using this facility
 * requires us to log "intent" items in case log recovery needs to
 * redo the operation, and to log "done" items to indicate that redo
 * is not necessary.
 *
 * Deferred work is tracked in xfs_defer_pending items.  Each pending
 * item tracks one type of deferred work.  Incoming work items (which
 * have not yet had an intent logged) are attached to a pending item
 * on the dop_intake list, where they wait for the caller to finish
 * the deferred operations.
 *
 * Finishing a set of deferred operations is an involved process.  To
 * start, we define "rolling a deferred-op transaction" as follows:
 *
 * > For each xfs_defer_pending item on the dop_intake list,
 *   - Sort the work items in AG order.  XFS locking
 *     order rules require us to lock buffers in AG order.
 *   - Create a log intent item for that type.
 *   - Attach it to the pending item.
 *   - Move the pending item from the dop_intake list to the
 *     dop_pending list.
 * > Roll the transaction.
 *
 * NOTE: To avoid exceeding the transaction reservation, we limit the
 * number of items that we attach to a given xfs_defer_pending.
 *
 * The actual finishing process looks like this:
 *
 * > For each xfs_defer_pending in the dop_pending list,
 *   - Roll the deferred-op transaction as above.
 *   - Create a log done item for that type, and attach it to the
 *     log intent item.
 *   - For each work item attached to the log intent item,
 *     * Perform the described action.
 *     * Attach the work item to the log done item.
 *     * If the result of doing the work was -EAGAIN, ->finish work
 *       wants a new transaction.  See the "Requesting a Fresh
 *       Transaction while Finishing Deferred Work" section below for
 *       details.
 *
 * The key here is that we must log an intent item for all pending
 * work items every time we roll the transaction, and that we must log
 * a done item as soon as the work is completed.  With this mechanism
 * we can perform complex remapping operations, chaining intent items
 * as needed.
 *
 * Requesting a Fresh Transaction while Finishing Deferred Work
 *
 * If ->finish_item decides that it needs a fresh transaction to
 * finish the work, it must ask its caller (xfs_defer_finish) for a
 * continuation.  The most likely cause of this circumstance are the
 * refcount adjust functions deciding that they've logged enough items
 * to be at risk of exceeding the transaction reservation.
 *
 * To get a fresh transaction, we want to log the existing log done
 * item to prevent the log intent item from replaying, immediately log
 * a new log intent item with the unfinished work items, roll the
 * transaction, and re-call ->finish_item wherever it left off.  The
 * log done item and the new log intent item must be in the same
 * transaction or atomicity cannot be guaranteed; defer_finish ensures
 * that this happens.
 *
 * This requires some coordination between ->finish_item and
 * defer_finish.  Upon deciding to request a new transaction,
 * ->finish_item should update the current work item to reflect the
 * unfinished work.  Next, it should reset the log done item's list
 * count to the number of items finished, and return -EAGAIN.
 * defer_finish sees the -EAGAIN, logs the new log intent item
 * with the remaining work items, and leaves the xfs_defer_pending
 * item at the head of the dop_work queue.  Then it rolls the
 * transaction and picks up processing where it left off.  It is
 * required that ->finish_item must be careful to leave enough
 * transaction reservation to fit the new log intent item.
 *
 * This is an example of remapping the extent (E, E+B) into file X at
 * offset A and dealing with the extent (C, C+B) already being mapped
 * there:
 * +-------------------------------------------------+
 * | Unmap file X startblock C offset A length B     | t0
 * | Intent to reduce refcount for extent (C, B)     |
 * | Intent to remove rmap (X, C, A, B)              |
 * | Intent to free extent (D, 1) (bmbt block)       |
 * | Intent to map (X, A, B) at startblock E         |
 * +-------------------------------------------------+
 * | Map file X startblock E offset A length B       | t1
 * | Done mapping (X, E, A, B)                       |
 * | Intent to increase refcount for extent (E, B)   |
 * | Intent to add rmap (X, E, A, B)                 |
 * +-------------------------------------------------+
 * | Reduce refcount for extent (C, B)               | t2
 * | Done reducing refcount for extent (C, 9)        |
 * | Intent to reduce refcount for extent (C+9, B-9) |
 * | (ran out of space after 9 refcount updates)     |
 * +-------------------------------------------------+
 * | Reduce refcount for extent (C+9, B+9)           | t3
 * | Done reducing refcount for extent (C+9, B-9)    |
 * | Increase refcount for extent (E, B)             |
 * | Done increasing refcount for extent (E, B)      |
 * | Intent to free extent (C, B)                    |
 * | Intent to free extent (F, 1) (refcountbt block) |
 * | Intent to remove rmap (F, 1, REFC)              |
 * +-------------------------------------------------+
 * | Remove rmap (X, C, A, B)                        | t4
 * | Done removing rmap (X, C, A, B)                 |
 * | Add rmap (X, E, A, B)                           |
 * | Done adding rmap (X, E, A, B)                   |
 * | Remove rmap (F, 1, REFC)                        |
 * | Done removing rmap (F, 1, REFC)                 |
 * +-------------------------------------------------+
 * | Free extent (C, B)                              | t5
 * | Done freeing extent (C, B)                      |
 * | Free extent (D, 1)                              |
 * | Done freeing extent (D, 1)                      |
 * | Free extent (F, 1)                              |
 * | Done freeing extent (F, 1)                      |
 * +-------------------------------------------------+
 *
 * If we should crash before t2 commits, log recovery replays
 * the following intent items:
 *
 * - Intent to reduce refcount for extent (C, B)
 * - Intent to remove rmap (X, C, A, B)
 * - Intent to free extent (D, 1) (bmbt block)
 * - Intent to increase refcount for extent (E, B)
 * - Intent to add rmap (X, E, A, B)
 *
 * In the process of recovering, it should also generate and take care
 * of these intent items:
 *
 * - Intent to free extent (C, B)
 * - Intent to free extent (F, 1) (refcountbt block)
 * - Intent to remove rmap (F, 1, REFC)
 *
 * Note that the continuation requested between t2 and t3 is likely to
 * reoccur.
 */

static const struct xfs_defer_op_type *defer_op_types[] = {
        [XFS_DEFER_OPS_TYPE_BMAP]       = &xfs_bmap_update_defer_type,
        [XFS_DEFER_OPS_TYPE_REFCOUNT]   = &xfs_refcount_update_defer_type,
        [XFS_DEFER_OPS_TYPE_RMAP]       = &xfs_rmap_update_defer_type,
        [XFS_DEFER_OPS_TYPE_FREE]       = &xfs_extent_free_defer_type,
        [XFS_DEFER_OPS_TYPE_AGFL_FREE]  = &xfs_agfl_free_defer_type,
};

static void
xfs_defer_create_intent(
        struct xfs_trans                *tp,
        struct xfs_defer_pending        *dfp,
        bool                            sort)
{
        const struct xfs_defer_op_type  *ops = defer_op_types[dfp->dfp_type];

        if (!dfp->dfp_intent)
                dfp->dfp_intent = ops->create_intent(tp, &dfp->dfp_work,
                                                     dfp->dfp_count, sort);
}

/*
 * For each pending item in the intake list, log its intent item and the
 * associated extents, then add the entire intake list to the end of
 * the pending list.
 */
STATIC void
xfs_defer_create_intents(
        struct xfs_trans                *tp)
{
        struct xfs_defer_pending        *dfp;

        list_for_each_entry(dfp, &tp->t_dfops, dfp_list) {
                trace_xfs_defer_create_intent(tp->t_mountp, dfp);
                xfs_defer_create_intent(tp, dfp, true);
        }
}

/* Abort all the intents that were committed. */
STATIC void
xfs_defer_trans_abort(
        struct xfs_trans                *tp,
        struct list_head                *dop_pending)
{
        struct xfs_defer_pending        *dfp;
        const struct xfs_defer_op_type  *ops;

        trace_xfs_defer_trans_abort(tp, _RET_IP_);

        /* Abort intent items that don't have a done item. */
        list_for_each_entry(dfp, dop_pending, dfp_list) {
                ops = defer_op_types[dfp->dfp_type];
                trace_xfs_defer_pending_abort(tp->t_mountp, dfp);
                if (dfp->dfp_intent && !dfp->dfp_done) {
                        ops->abort_intent(dfp->dfp_intent);
                        dfp->dfp_intent = NULL;
                }
        }
}

/*
 * Capture resources that the caller said not to release ("held") when the
 * transaction commits.  Caller is responsible for zero-initializing @dres.
 */
static int
xfs_defer_save_resources(
        struct xfs_defer_resources      *dres,
        struct xfs_trans                *tp)
{
        struct xfs_buf_log_item         *bli;
        struct xfs_inode_log_item       *ili;
        struct xfs_log_item             *lip;

        BUILD_BUG_ON(NBBY * sizeof(dres->dr_ordered) < XFS_DEFER_OPS_NR_BUFS);

        list_for_each_entry(lip, &tp->t_items, li_trans) {
                switch (lip->li_type) {
                case XFS_LI_BUF:
                        bli = container_of(lip, struct xfs_buf_log_item,
                                           bli_item);
                        if (bli->bli_flags & XFS_BLI_HOLD) {
                                if (dres->dr_bufs >= XFS_DEFER_OPS_NR_BUFS) {
                                        ASSERT(0);
                                        return -EFSCORRUPTED;
                                }
                                if (bli->bli_flags & XFS_BLI_ORDERED)
                                        dres->dr_ordered |=
                                                        (1U << dres->dr_bufs);
                                else
                                        xfs_trans_dirty_buf(tp, bli->bli_buf);
                                dres->dr_bp[dres->dr_bufs++] = bli->bli_buf;
                        }
                        break;
                case XFS_LI_INODE:
                        ili = container_of(lip, struct xfs_inode_log_item,
                                           ili_item);
                        if (ili->ili_lock_flags == 0) {
                                if (dres->dr_inos >= XFS_DEFER_OPS_NR_INODES) {
                                        ASSERT(0);
                                        return -EFSCORRUPTED;
                                }
                                xfs_trans_log_inode(tp, ili->ili_inode,
                                                    XFS_ILOG_CORE);
                                dres->dr_ip[dres->dr_inos++] = ili->ili_inode;
                        }
                        break;
                default:
                        break;
                }
        }

        return 0;
}

/* Attach the held resources to the transaction. */
static void
xfs_defer_restore_resources(
        struct xfs_trans                *tp,
        struct xfs_defer_resources      *dres)
{
        unsigned short                  i;

        /* Rejoin the joined inodes. */
        for (i = 0; i < dres->dr_inos; i++)
                xfs_trans_ijoin(tp, dres->dr_ip[i], 0);

        /* Rejoin the buffers and dirty them so the log moves forward. */
        for (i = 0; i < dres->dr_bufs; i++) {
                xfs_trans_bjoin(tp, dres->dr_bp[i]);
                if (dres->dr_ordered & (1U << i))
                        xfs_trans_ordered_buf(tp, dres->dr_bp[i]);
                xfs_trans_bhold(tp, dres->dr_bp[i]);
        }
}

/* Roll a transaction so we can do some deferred op processing. */
STATIC int
xfs_defer_trans_roll(
        struct xfs_trans                **tpp)
{
        struct xfs_defer_resources      dres = { };
        int                             error;

        error = xfs_defer_save_resources(&dres, *tpp);
        if (error)
                return error;

        trace_xfs_defer_trans_roll(*tpp, _RET_IP_);

        /*
         * Roll the transaction.  Rolling always given a new transaction (even
         * if committing the old one fails!) to hand back to the caller, so we
         * join the held resources to the new transaction so that we always
         * return with the held resources joined to @tpp, no matter what
         * happened.
         */
        error = xfs_trans_roll(tpp);

        xfs_defer_restore_resources(*tpp, &dres);

        if (error)
                trace_xfs_defer_trans_roll_error(*tpp, error);
        return error;
}

/*
 * Free up any items left in the list.
 */
static void
xfs_defer_cancel_list(
        struct xfs_mount                *mp,
        struct list_head                *dop_list)
{
        struct xfs_defer_pending        *dfp;
        struct xfs_defer_pending        *pli;
        struct list_head                *pwi;
        struct list_head                *n;
        const struct xfs_defer_op_type  *ops;

        /*
         * Free the pending items.  Caller should already have arranged
         * for the intent items to be released.
         */
        list_for_each_entry_safe(dfp, pli, dop_list, dfp_list) {
                ops = defer_op_types[dfp->dfp_type];
                trace_xfs_defer_cancel_list(mp, dfp);
                list_del(&dfp->dfp_list);
                list_for_each_safe(pwi, n, &dfp->dfp_work) {
                        list_del(pwi);
                        dfp->dfp_count--;
                        ops->cancel_item(pwi);
                }
                ASSERT(dfp->dfp_count == 0);
                kmem_cache_free(xfs_defer_pending_cache, dfp);
        }
}

/*
 * Prevent a log intent item from pinning the tail of the log by logging a
 * done item to release the intent item; and then log a new intent item.
 * The caller should provide a fresh transaction and roll it after we're done.
 */
static int
xfs_defer_relog(
        struct xfs_trans                **tpp,
        struct list_head                *dfops)
{
        struct xlog                     *log = (*tpp)->t_mountp->m_log;
        struct xfs_defer_pending        *dfp;
        xfs_lsn_t                       threshold_lsn = NULLCOMMITLSN;


        ASSERT((*tpp)->t_flags & XFS_TRANS_PERM_LOG_RES);

        list_for_each_entry(dfp, dfops, dfp_list) {
                /*
                 * If the log intent item for this deferred op is not a part of
                 * the current log checkpoint, relog the intent item to keep
                 * the log tail moving forward.  We're ok with this being racy
                 * because an incorrect decision means we'll be a little slower
                 * at pushing the tail.
                 */
                if (dfp->dfp_intent == NULL ||
                    xfs_log_item_in_current_chkpt(dfp->dfp_intent))
                        continue;

                /*
                 * Figure out where we need the tail to be in order to maintain
                 * the minimum required free space in the log.  Only sample
                 * the log threshold once per call.
                 */
                if (threshold_lsn == NULLCOMMITLSN) {
                        threshold_lsn = xlog_grant_push_threshold(log, 0);
                        if (threshold_lsn == NULLCOMMITLSN)
                                break;
                }
                if (XFS_LSN_CMP(dfp->dfp_intent->li_lsn, threshold_lsn) >= 0)
                        continue;

                trace_xfs_defer_relog_intent((*tpp)->t_mountp, dfp);
                XFS_STATS_INC((*tpp)->t_mountp, defer_relog);
                dfp->dfp_intent = xfs_trans_item_relog(dfp->dfp_intent, *tpp);
        }

        if ((*tpp)->t_flags & XFS_TRANS_DIRTY)
                return xfs_defer_trans_roll(tpp);
        return 0;
}

/*
 * Log an intent-done item for the first pending intent, and finish the work
 * items.
 */
static int
xfs_defer_finish_one(
        struct xfs_trans                *tp,
        struct xfs_defer_pending        *dfp)
{
        const struct xfs_defer_op_type  *ops = defer_op_types[dfp->dfp_type];
        struct xfs_btree_cur            *state = NULL;
        struct list_head                *li, *n;
        int                             error;

        trace_xfs_defer_pending_finish(tp->t_mountp, dfp);

        dfp->dfp_done = ops->create_done(tp, dfp->dfp_intent, dfp->dfp_count);
        list_for_each_safe(li, n, &dfp->dfp_work) {
                list_del(li);
                dfp->dfp_count--;
                error = ops->finish_item(tp, dfp->dfp_done, li, &state);
                if (error == -EAGAIN) {
                        /*
                         * Caller wants a fresh transaction; put the work item
                         * back on the list and log a new log intent item to
                         * replace the old one.  See "Requesting a Fresh
                         * Transaction while Finishing Deferred Work" above.
                         */
                        list_add(li, &dfp->dfp_work);
                        dfp->dfp_count++;
                        dfp->dfp_done = NULL;
                        dfp->dfp_intent = NULL;
                        xfs_defer_create_intent(tp, dfp, false);
                }

                if (error)
                        goto out;
        }

        /* Done with the dfp, free it. */
        list_del(&dfp->dfp_list);
        kmem_cache_free(xfs_defer_pending_cache, dfp);
out:
        if (ops->finish_cleanup)
                ops->finish_cleanup(tp, state, error);
        return error;
}

/*
 * Finish all the pending work.  This involves logging intent items for
 * any work items that wandered in since the last transaction roll (if
 * one has even happened), rolling the transaction, and finishing the
 * work items in the first item on the logged-and-pending list.
 *
 * If an inode is provided, relog it to the new transaction.
 */
int
xfs_defer_finish_noroll(
        struct xfs_trans                **tp)
{
        struct xfs_defer_pending        *dfp;
        int                             error = 0;
        LIST_HEAD(dop_pending);

        ASSERT((*tp)->t_flags & XFS_TRANS_PERM_LOG_RES);

        trace_xfs_defer_finish(*tp, _RET_IP_);

        /* Until we run out of pending work to finish... */
        while (!list_empty(&dop_pending) || !list_empty(&(*tp)->t_dfops)) {
                /*
                 * Deferred items that are created in the process of finishing
                 * other deferred work items should be queued at the head of
                 * the pending list, which puts them ahead of the deferred work
                 * that was created by the caller.  This keeps the number of
                 * pending work items to a minimum, which decreases the amount
                 * of time that any one intent item can stick around in memory,
                 * pinning the log tail.
                 */
                xfs_defer_create_intents(*tp);
                list_splice_init(&(*tp)->t_dfops, &dop_pending);

                error = xfs_defer_trans_roll(tp);
                if (error)
                        goto out_shutdown;

                /* Possibly relog intent items to keep the log moving. */
                error = xfs_defer_relog(tp, &dop_pending);
                if (error)
                        goto out_shutdown;

                dfp = list_first_entry(&dop_pending, struct xfs_defer_pending,
                                       dfp_list);
                error = xfs_defer_finish_one(*tp, dfp);
                if (error && error != -EAGAIN)
                        goto out_shutdown;
        }

        trace_xfs_defer_finish_done(*tp, _RET_IP_);
        return 0;

out_shutdown:
        xfs_defer_trans_abort(*tp, &dop_pending);
        xfs_force_shutdown((*tp)->t_mountp, SHUTDOWN_CORRUPT_INCORE);
        trace_xfs_defer_finish_error(*tp, error);
        xfs_defer_cancel_list((*tp)->t_mountp, &dop_pending);
        xfs_defer_cancel(*tp);
        return error;
}

int
xfs_defer_finish(
        struct xfs_trans        **tp)
{
        int                     error;

        /*
         * Finish and roll the transaction once more to avoid returning to the
         * caller with a dirty transaction.
         */
        error = xfs_defer_finish_noroll(tp);
        if (error)
                return error;
        if ((*tp)->t_flags & XFS_TRANS_DIRTY) {
                error = xfs_defer_trans_roll(tp);
                if (error) {
                        xfs_force_shutdown((*tp)->t_mountp,
                                           SHUTDOWN_CORRUPT_INCORE);
                        return error;
                }
        }

        /* Reset LOWMODE now that we've finished all the dfops. */
        ASSERT(list_empty(&(*tp)->t_dfops));
        (*tp)->t_flags &= ~XFS_TRANS_LOWMODE;
        return 0;
}

void
xfs_defer_cancel(
        struct xfs_trans        *tp)
{
        struct xfs_mount        *mp = tp->t_mountp;

        trace_xfs_defer_cancel(tp, _RET_IP_);
        xfs_defer_cancel_list(mp, &tp->t_dfops);
}

/* Add an item for later deferred processing. */
void
xfs_defer_add(
        struct xfs_trans                *tp,
        enum xfs_defer_ops_type         type,
        struct list_head                *li)
{
        struct xfs_defer_pending        *dfp = NULL;
        const struct xfs_defer_op_type  *ops;

        ASSERT(tp->t_flags & XFS_TRANS_PERM_LOG_RES);
        BUILD_BUG_ON(ARRAY_SIZE(defer_op_types) != XFS_DEFER_OPS_TYPE_MAX);

        /*
         * Add the item to a pending item at the end of the intake list.
         * If the last pending item has the same type, reuse it.  Else,
         * create a new pending item at the end of the intake list.
         */
        if (!list_empty(&tp->t_dfops)) {
                dfp = list_last_entry(&tp->t_dfops,
                                struct xfs_defer_pending, dfp_list);
                ops = defer_op_types[dfp->dfp_type];
                if (dfp->dfp_type != type ||
                    (ops->max_items && dfp->dfp_count >= ops->max_items))
                        dfp = NULL;
        }
        if (!dfp) {
                dfp = kmem_cache_zalloc(xfs_defer_pending_cache,
                                GFP_NOFS | __GFP_NOFAIL);
                dfp->dfp_type = type;
                dfp->dfp_intent = NULL;
                dfp->dfp_done = NULL;
                dfp->dfp_count = 0;
                INIT_LIST_HEAD(&dfp->dfp_work);
                list_add_tail(&dfp->dfp_list, &tp->t_dfops);
        }

        list_add_tail(li, &dfp->dfp_work);
        dfp->dfp_count++;
}

/*
 * Move deferred ops from one transaction to another and reset the source to
 * initial state. This is primarily used to carry state forward across
 * transaction rolls with pending dfops.
 */
void
xfs_defer_move(
        struct xfs_trans        *dtp,
        struct xfs_trans        *stp)
{
        list_splice_init(&stp->t_dfops, &dtp->t_dfops);

        /*
         * Low free space mode was historically controlled by a dfops field.
         * This meant that low mode state potentially carried across multiple
         * transaction rolls. Transfer low mode on a dfops move to preserve
         * that behavior.
         */
        dtp->t_flags |= (stp->t_flags & XFS_TRANS_LOWMODE);
        stp->t_flags &= ~XFS_TRANS_LOWMODE;
}

/*
 * Prepare a chain of fresh deferred ops work items to be completed later.  Log
 * recovery requires the ability to put off until later the actual finishing
 * work so that it can process unfinished items recovered from the log in
 * correct order.
 *
 * Create and log intent items for all the work that we're capturing so that we
 * can be assured that the items will get replayed if the system goes down
 * before log recovery gets a chance to finish the work it put off.  The entire
 * deferred ops state is transferred to the capture structure and the
 * transaction is then ready for the caller to commit it.  If there are no
 * intent items to capture, this function returns NULL.
 *
 * If capture_ip is not NULL, the capture structure will obtain an extra
 * reference to the inode.
 */
static struct xfs_defer_capture *
xfs_defer_ops_capture(
        struct xfs_trans                *tp)
{
        struct xfs_defer_capture        *dfc;
        unsigned short                  i;
        int                             error;

        if (list_empty(&tp->t_dfops))
                return NULL;

        /* Create an object to capture the defer ops. */
        dfc = kmem_zalloc(sizeof(*dfc), KM_NOFS);
        INIT_LIST_HEAD(&dfc->dfc_list);
        INIT_LIST_HEAD(&dfc->dfc_dfops);

        xfs_defer_create_intents(tp);

        /* Move the dfops chain and transaction state to the capture struct. */
        list_splice_init(&tp->t_dfops, &dfc->dfc_dfops);
        dfc->dfc_tpflags = tp->t_flags & XFS_TRANS_LOWMODE;
        tp->t_flags &= ~XFS_TRANS_LOWMODE;

        /* Capture the remaining block reservations along with the dfops. */
        dfc->dfc_blkres = tp->t_blk_res - tp->t_blk_res_used;
        dfc->dfc_rtxres = tp->t_rtx_res - tp->t_rtx_res_used;

        /* Preserve the log reservation size. */
        dfc->dfc_logres = tp->t_log_res;

        error = xfs_defer_save_resources(&dfc->dfc_held, tp);
        if (error) {
                /*
                 * Resource capture should never fail, but if it does, we
                 * still have to shut down the log and release things
                 * properly.
                 */
                xfs_force_shutdown(tp->t_mountp, SHUTDOWN_CORRUPT_INCORE);
        }

        /*
         * Grab extra references to the inodes and buffers because callers are
         * expected to release their held references after we commit the
         * transaction.
         */
        for (i = 0; i < dfc->dfc_held.dr_inos; i++) {
                ASSERT(xfs_isilocked(dfc->dfc_held.dr_ip[i], XFS_ILOCK_EXCL));
                ihold(VFS_I(dfc->dfc_held.dr_ip[i]));
        }

        for (i = 0; i < dfc->dfc_held.dr_bufs; i++)
                xfs_buf_hold(dfc->dfc_held.dr_bp[i]);

        return dfc;
}

/* Release all resources that we used to capture deferred ops. */
void
xfs_defer_ops_capture_free(
        struct xfs_mount                *mp,
        struct xfs_defer_capture        *dfc)
{
        unsigned short                  i;

        xfs_defer_cancel_list(mp, &dfc->dfc_dfops);

        for (i = 0; i < dfc->dfc_held.dr_bufs; i++)
                xfs_buf_relse(dfc->dfc_held.dr_bp[i]);

        for (i = 0; i < dfc->dfc_held.dr_inos; i++)
                xfs_irele(dfc->dfc_held.dr_ip[i]);

        kmem_free(dfc);
}

/*
 * Capture any deferred ops and commit the transaction.  This is the last step
 * needed to finish a log intent item that we recovered from the log.  If any
 * of the deferred ops operate on an inode, the caller must pass in that inode
 * so that the reference can be transferred to the capture structure.  The
 * caller must hold ILOCK_EXCL on the inode, and must unlock it before calling
 * xfs_defer_ops_continue.
 */
int
xfs_defer_ops_capture_and_commit(
        struct xfs_trans                *tp,
        struct list_head                *capture_list)
{
        struct xfs_mount                *mp = tp->t_mountp;
        struct xfs_defer_capture        *dfc;
        int                             error;

        /* If we don't capture anything, commit transaction and exit. */
        dfc = xfs_defer_ops_capture(tp);
        if (!dfc)
                return xfs_trans_commit(tp);

        /* Commit the transaction and add the capture structure to the list. */
        error = xfs_trans_commit(tp);
        if (error) {
                xfs_defer_ops_capture_free(mp, dfc);
                return error;
        }

        list_add_tail(&dfc->dfc_list, capture_list);
        return 0;
}

/*
 * Attach a chain of captured deferred ops to a new transaction and free the
 * capture structure.  If an inode was captured, it will be passed back to the
 * caller with ILOCK_EXCL held and joined to the transaction with lockflags==0.
 * The caller now owns the inode reference.
 */
void
xfs_defer_ops_continue(
        struct xfs_defer_capture        *dfc,
        struct xfs_trans                *tp,
        struct xfs_defer_resources      *dres)
{
        ASSERT(tp->t_flags & XFS_TRANS_PERM_LOG_RES);
        ASSERT(!(tp->t_flags & XFS_TRANS_DIRTY));

        /* Lock and join the captured inode to the new transaction. */
        if (dfc->dfc_held.dr_inos == 2)
                xfs_lock_two_inodes(dfc->dfc_held.dr_ip[0], XFS_ILOCK_EXCL,
                                    dfc->dfc_held.dr_ip[1], XFS_ILOCK_EXCL);
        else if (dfc->dfc_held.dr_inos == 1)
                xfs_ilock(dfc->dfc_held.dr_ip[0], XFS_ILOCK_EXCL);
        xfs_defer_restore_resources(tp, &dfc->dfc_held);
        memcpy(dres, &dfc->dfc_held, sizeof(struct xfs_defer_resources));

        /* Move captured dfops chain and state to the transaction. */
        list_splice_init(&dfc->dfc_dfops, &tp->t_dfops);
        tp->t_flags |= dfc->dfc_tpflags;

        kmem_free(dfc);
}

/* Release the resources captured and continued during recovery. */
void
xfs_defer_resources_rele(
        struct xfs_defer_resources      *dres)
{
        unsigned short                  i;

        for (i = 0; i < dres->dr_inos; i++) {
                xfs_iunlock(dres->dr_ip[i], XFS_ILOCK_EXCL);
                xfs_irele(dres->dr_ip[i]);
                dres->dr_ip[i] = NULL;
        }

        for (i = 0; i < dres->dr_bufs; i++) {
                xfs_buf_relse(dres->dr_bp[i]);
                dres->dr_bp[i] = NULL;
        }

        dres->dr_inos = 0;
        dres->dr_bufs = 0;
        dres->dr_ordered = 0;
}

static inline int __init
xfs_defer_init_cache(void)
{
        xfs_defer_pending_cache = kmem_cache_create("xfs_defer_pending",
                        sizeof(struct xfs_defer_pending),
                        0, 0, NULL);

        return xfs_defer_pending_cache != NULL ? 0 : -ENOMEM;
}

static inline void
xfs_defer_destroy_cache(void)
{
        kmem_cache_destroy(xfs_defer_pending_cache);
        xfs_defer_pending_cache = NULL;
}

/* Set up caches for deferred work items. */
int __init
xfs_defer_init_item_caches(void)
{
        int                             error;

        error = xfs_defer_init_cache();
        if (error)
                return error;
        error = xfs_rmap_intent_init_cache();
        if (error)
                goto err;
        error = xfs_refcount_intent_init_cache();
        if (error)
                goto err;
        error = xfs_bmap_intent_init_cache();
        if (error)
                goto err;
        error = xfs_extfree_intent_init_cache();
        if (error)
                goto err;

        return 0;
err:
        xfs_defer_destroy_item_caches();
        return error;
}

/* Destroy all the deferred work item caches, if they've been allocated. */
void
xfs_defer_destroy_item_caches(void)
{
        xfs_extfree_intent_destroy_cache();
        xfs_bmap_intent_destroy_cache();
        xfs_refcount_intent_destroy_cache();
        xfs_rmap_intent_destroy_cache();
        xfs_defer_destroy_cache();
}