Adding upstream version 6.6.15.upstream/6.6.15

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 932 insertions, 0 deletions

diff --git a/fs/xfs/libxfs/xfs_defer.c b/fs/xfs/libxfs/xfs_defer.c
new file mode 100644
index 000000000..bcfb6a420
--- /dev/null
+++ b/fs/xfs/libxfs/xfs_defer.c
@@ -0,0 +1,932 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (C) 2016 Oracle.  All Rights Reserved.
+ * Author: Darrick J. Wong <darrick.wong@oracle.com>
+ */
+#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"
+#include "xfs_buf.h"
+#include "xfs_da_format.h"
+#include "xfs_da_btree.h"
+#include "xfs_attr.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,
+	[XFS_DEFER_OPS_TYPE_ATTR]	= &xfs_attr_defer_type,
+};
+
+/*
+ * Ensure there's a log intent item associated with this deferred work item if
+ * the operation must be restarted on crash.  Returns 1 if there's a log item;
+ * 0 if there isn't; or a negative errno.
+ */
+static int
+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];
+	struct xfs_log_item		*lip;
+
+	if (dfp->dfp_intent)
+		return 1;
+
+	lip = ops->create_intent(tp, &dfp->dfp_work, dfp->dfp_count, sort);
+	if (!lip)
+		return 0;
+	if (IS_ERR(lip))
+		return PTR_ERR(lip);
+
+	dfp->dfp_intent = lip;
+	return 1;
+}
+
+/*
+ * 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.
+ *
+ * Returns 1 if at least one log item was associated with the deferred work;
+ * 0 if there are no log items; or a negative errno.
+ */
+static int
+xfs_defer_create_intents(
+	struct xfs_trans		*tp)
+{
+	struct xfs_defer_pending	*dfp;
+	int				ret = 0;
+
+	list_for_each_entry(dfp, &tp->t_dfops, dfp_list) {
+		int			ret2;
+
+		trace_xfs_defer_create_intent(tp->t_mountp, dfp);
+		ret2 = xfs_defer_create_intent(tp, dfp, true);
+		if (ret2 < 0)
+			return ret2;
+		ret |= ret2;
+	}
+	return ret;
+}
+
+/* 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--;
+			trace_xfs_defer_cancel_item(mp, dfp, pwi);
+			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--;
+		trace_xfs_defer_finish_item(tp->t_mountp, dfp, li);
+		error = ops->finish_item(tp, dfp->dfp_done, li, &state);
+		if (error == -EAGAIN) {
+			int		ret;
+
+			/*
+			 * 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;
+			ret = xfs_defer_create_intent(tp, dfp, false);
+			if (ret < 0)
+				error = ret;
+		}
+
+		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 = NULL;
+	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.
+		 */
+		int has_intents = xfs_defer_create_intents(*tp);
+
+		list_splice_init(&(*tp)->t_dfops, &dop_pending);
+
+		if (has_intents < 0) {
+			error = has_intents;
+			goto out_shutdown;
+		}
+		if (has_intents || dfp) {
+			error = xfs_defer_trans_roll(tp);
+			if (error)
+				goto out_shutdown;
+
+			/* 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 = defer_op_types[type];
+
+	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);
+		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);
+	trace_xfs_defer_add_item(tp->t_mountp, dfp, li);
+	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;
+
+	error = xfs_defer_create_intents(tp);
+	if (error < 0)
+		return ERR_PTR(error);
+
+	/* 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);
+
+	/* 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 (IS_ERR(dfc)) {
+		xfs_trans_cancel(tp);
+		return PTR_ERR(dfc);
+	}
+	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)
+{
+	unsigned int			i;
+
+	ASSERT(tp->t_flags & XFS_TRANS_PERM_LOG_RES);
+	ASSERT(!(tp->t_flags & XFS_TRANS_DIRTY));
+
+	/* Lock the captured resources 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);
+
+	for (i = 0; i < dfc->dfc_held.dr_bufs; i++)
+		xfs_buf_lock(dfc->dfc_held.dr_bp[i]);
+
+	/* Join the captured resources to the new transaction. */
+	xfs_defer_restore_resources(tp, &dfc->dfc_held);
+	memcpy(dres, &dfc->dfc_held, sizeof(struct xfs_defer_resources));
+	dres->dr_bufs = 0;
+
+	/* 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;
+	error = xfs_attr_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_attr_intent_destroy_cache();
+	xfs_extfree_intent_destroy_cache();
+	xfs_bmap_intent_destroy_cache();
+	xfs_refcount_intent_destroy_cache();
+	xfs_rmap_intent_destroy_cache();
+	xfs_defer_destroy_cache();
+}