10 files changed, 551 insertions, 11 deletions

diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
index 8758000d82d2..e4bf2c406e3b 100644
--- a/fs/xfs/libxfs/xfs_bmap.c
+++ b/fs/xfs/libxfs/xfs_bmap.c
@@ -4631,6 +4631,17 @@ xfs_bmapi_write(
 				goto error0;
 			if (bma.blkno == NULLFSBLOCK)
 				break;
+
+			/*
+			 * If this is a CoW allocation, record the data in
+			 * the refcount btree for orphan recovery.
+			 */
+			if (whichfork == XFS_COW_FORK) {
+				error = xfs_refcount_alloc_cow_extent(mp, dfops,
+						bma.blkno, bma.length);
+				if (error)
+					goto error0;
+			}
 		}
 
 		/* Deal with the allocated space we found.  */
diff --git a/fs/xfs/libxfs/xfs_format.h b/fs/xfs/libxfs/xfs_format.h
index 8b826102dfe3..777fa974a319 100644
--- a/fs/xfs/libxfs/xfs_format.h
+++ b/fs/xfs/libxfs/xfs_format.h
@@ -1375,7 +1375,8 @@ struct xfs_owner_info {
 #define XFS_RMAP_OWN_INOBT	(-6ULL)	/* Inode btree blocks */
 #define XFS_RMAP_OWN_INODES	(-7ULL)	/* Inode chunk */
 #define XFS_RMAP_OWN_REFC	(-8ULL) /* refcount tree */
-#define XFS_RMAP_OWN_MIN	(-9ULL) /* guard */
+#define XFS_RMAP_OWN_COW	(-9ULL) /* cow allocations */
+#define XFS_RMAP_OWN_MIN	(-10ULL) /* guard */
 
 #define XFS_RMAP_NON_INODE_OWNER(owner)	(!!((owner) & (1ULL << 63)))
 
@@ -1477,6 +1478,17 @@ unsigned int xfs_refc_block(struct xfs_mount *mp);
  * data) are not tracked here.  Free space is also not tracked here.
  * This is consistent with pre-reflink XFS.
  */
+
+/*
+ * Extents that are being used to stage a copy on write are stored
+ * in the refcount btree with a refcount of 1 and the upper bit set
+ * on the startblock.  This speeds up mount time deletion of stale
+ * staging extents because they're all at the right side of the tree.
+ */
+#define XFS_REFC_COW_START		((xfs_agblock_t)(1U << 31))
+#define REFCNTBT_COWFLAG_BITLEN		1
+#define REFCNTBT_AGBLOCK_BITLEN		31
+
 struct xfs_refcount_rec {
 	__be32		rc_startblock;	/* starting block number */
 	__be32		rc_blockcount;	/* count of blocks */
diff --git a/fs/xfs/libxfs/xfs_refcount.c b/fs/xfs/libxfs/xfs_refcount.c
index ab8c30d2a605..56bfef116423 100644
--- a/fs/xfs/libxfs/xfs_refcount.c
+++ b/fs/xfs/libxfs/xfs_refcount.c
@@ -36,13 +36,23 @@
 #include "xfs_trans.h"
 #include "xfs_bit.h"
 #include "xfs_refcount.h"
+#include "xfs_rmap.h"
 
 /* Allowable refcount adjustment amounts. */
 enum xfs_refc_adjust_op {
 	XFS_REFCOUNT_ADJUST_INCREASE	= 1,
 	XFS_REFCOUNT_ADJUST_DECREASE	= -1,
+	XFS_REFCOUNT_ADJUST_COW_ALLOC	= 0,
+	XFS_REFCOUNT_ADJUST_COW_FREE	= -1,
 };
 
+STATIC int __xfs_refcount_cow_alloc(struct xfs_btree_cur *rcur,
+		xfs_agblock_t agbno, xfs_extlen_t aglen,
+		struct xfs_defer_ops *dfops);
+STATIC int __xfs_refcount_cow_free(struct xfs_btree_cur *rcur,
+		xfs_agblock_t agbno, xfs_extlen_t aglen,
+		struct xfs_defer_ops *dfops);
+
 /*
  * Look up the first record less than or equal to [bno, len] in the btree
  * given by cur.
@@ -77,6 +87,17 @@ xfs_refcount_lookup_ge(
 	return xfs_btree_lookup(cur, XFS_LOOKUP_GE, stat);
 }
 
+/* Convert on-disk record to in-core format. */
+static inline void
+xfs_refcount_btrec_to_irec(
+	union xfs_btree_rec		*rec,
+	struct xfs_refcount_irec	*irec)
+{
+	irec->rc_startblock = be32_to_cpu(rec->refc.rc_startblock);
+	irec->rc_blockcount = be32_to_cpu(rec->refc.rc_blockcount);
+	irec->rc_refcount = be32_to_cpu(rec->refc.rc_refcount);
+}
+
 /*
  * Get the data from the pointed-to record.
  */
@@ -86,14 +107,12 @@ xfs_refcount_get_rec(
 	struct xfs_refcount_irec	*irec,
 	int				*stat)
 {
-	union xfs_btree_rec	*rec;
-	int			error;
+	union xfs_btree_rec		*rec;
+	int				error;
 
 	error = xfs_btree_get_rec(cur, &rec, stat);
 	if (!error && *stat == 1) {
-		irec->rc_startblock = be32_to_cpu(rec->refc.rc_startblock);
-		irec->rc_blockcount = be32_to_cpu(rec->refc.rc_blockcount);
-		irec->rc_refcount = be32_to_cpu(rec->refc.rc_refcount);
+		xfs_refcount_btrec_to_irec(rec, irec);
 		trace_xfs_refcount_get(cur->bc_mp, cur->bc_private.a.agno,
 				irec);
 	}
@@ -501,6 +520,8 @@ out_error:
 	return error;
 }
 
+#define XFS_FIND_RCEXT_SHARED	1
+#define XFS_FIND_RCEXT_COW	2
 /*
  * Find the left extent and the one after it (cleft).  This function assumes
  * that we've already split any extent crossing agbno.
@@ -511,7 +532,8 @@ xfs_refcount_find_left_extents(
 	struct xfs_refcount_irec	*left,
 	struct xfs_refcount_irec	*cleft,
 	xfs_agblock_t			agbno,
-	xfs_extlen_t			aglen)
+	xfs_extlen_t			aglen,
+	int				flags)
 {
 	struct xfs_refcount_irec	tmp;
 	int				error;
@@ -531,6 +553,10 @@ xfs_refcount_find_left_extents(
 
 	if (xfs_refc_next(&tmp) != agbno)
 		return 0;
+	if ((flags & XFS_FIND_RCEXT_SHARED) && tmp.rc_refcount < 2)
+		return 0;
+	if ((flags & XFS_FIND_RCEXT_COW) && tmp.rc_refcount > 1)
+		return 0;
 	/* We have a left extent; retrieve (or invent) the next right one */
 	*left = tmp;
 
@@ -590,7 +616,8 @@ xfs_refcount_find_right_extents(
 	struct xfs_refcount_irec	*right,
 	struct xfs_refcount_irec	*cright,
 	xfs_agblock_t			agbno,
-	xfs_extlen_t			aglen)
+	xfs_extlen_t			aglen,
+	int				flags)
 {
 	struct xfs_refcount_irec	tmp;
 	int				error;
@@ -610,6 +637,10 @@ xfs_refcount_find_right_extents(
 
 	if (tmp.rc_startblock != agbno + aglen)
 		return 0;
+	if ((flags & XFS_FIND_RCEXT_SHARED) && tmp.rc_refcount < 2)
+		return 0;
+	if ((flags & XFS_FIND_RCEXT_COW) && tmp.rc_refcount > 1)
+		return 0;
 	/* We have a right extent; retrieve (or invent) the next left one */
 	*right = tmp;
 
@@ -676,6 +707,7 @@ xfs_refcount_merge_extents(
 	xfs_agblock_t		*agbno,
 	xfs_extlen_t		*aglen,
 	enum xfs_refc_adjust_op adjust,
+	int			flags,
 	bool			*shape_changed)
 {
 	struct xfs_refcount_irec	left = {0}, cleft = {0};
@@ -691,11 +723,11 @@ xfs_refcount_merge_extents(
 	 * [right].
 	 */
 	error = xfs_refcount_find_left_extents(cur, &left, &cleft, *agbno,
-			*aglen);
+			*aglen, flags);
 	if (error)
 		return error;
 	error = xfs_refcount_find_right_extents(cur, &right, &cright, *agbno,
-			*aglen);
+			*aglen, flags);
 	if (error)
 		return error;
 
@@ -968,7 +1000,7 @@ xfs_refcount_adjust(
 	 * Try to merge with the left or right extents of the range.
 	 */
 	error = xfs_refcount_merge_extents(cur, new_agbno, new_aglen, adj,
-			&shape_changed);
+			XFS_FIND_RCEXT_SHARED, &shape_changed);
 	if (error)
 		goto out_error;
 	if (shape_changed)
@@ -1089,6 +1121,16 @@ xfs_refcount_finish_one(
 			new_len, XFS_REFCOUNT_ADJUST_DECREASE, dfops, NULL);
 		*new_fsb = XFS_AGB_TO_FSB(mp, agno, new_agbno);
 		break;
+	case XFS_REFCOUNT_ALLOC_COW:
+		*new_fsb = startblock + blockcount;
+		*new_len = 0;
+		error = __xfs_refcount_cow_alloc(rcur, bno, blockcount, dfops);
+		break;
+	case XFS_REFCOUNT_FREE_COW:
+		*new_fsb = startblock + blockcount;
+		*new_len = 0;
+		error = __xfs_refcount_cow_free(rcur, bno, blockcount, dfops);
+		break;
 	default:
 		ASSERT(0);
 		error = -EFSCORRUPTED;
@@ -1265,3 +1307,394 @@ out_error:
 				cur->bc_private.a.agno, error, _RET_IP_);
 	return error;
 }
+
+/*
+ * Recovering CoW Blocks After a Crash
+ *
+ * Due to the way that the copy on write mechanism works, there's a window of
+ * opportunity in which we can lose track of allocated blocks during a crash.
+ * Because CoW uses delayed allocation in the in-core CoW fork, writeback
+ * causes blocks to be allocated and stored in the CoW fork.  The blocks are
+ * no longer in the free space btree but are not otherwise recorded anywhere
+ * until the write completes and the blocks are mapped into the file.  A crash
+ * in between allocation and remapping results in the replacement blocks being
+ * lost.  This situation is exacerbated by the CoW extent size hint because
+ * allocations can hang around for long time.
+ *
+ * However, there is a place where we can record these allocations before they
+ * become mappings -- the reference count btree.  The btree does not record
+ * extents with refcount == 1, so we can record allocations with a refcount of
+ * 1.  Blocks being used for CoW writeout cannot be shared, so there should be
+ * no conflict with shared block records.  These mappings should be created
+ * when we allocate blocks to the CoW fork and deleted when they're removed
+ * from the CoW fork.
+ *
+ * Minor nit: records for in-progress CoW allocations and records for shared
+ * extents must never be merged, to preserve the property that (except for CoW
+ * allocations) there are no refcount btree entries with refcount == 1.  The
+ * only time this could potentially happen is when unsharing a block that's
+ * adjacent to CoW allocations, so we must be careful to avoid this.
+ *
+ * At mount time we recover lost CoW allocations by searching the refcount
+ * btree for these refcount == 1 mappings.  These represent CoW allocations
+ * that were in progress at the time the filesystem went down, so we can free
+ * them to get the space back.
+ *
+ * This mechanism is superior to creating EFIs for unmapped CoW extents for
+ * several reasons -- first, EFIs pin the tail of the log and would have to be
+ * periodically relogged to avoid filling up the log.  Second, CoW completions
+ * will have to file an EFD and create new EFIs for whatever remains in the
+ * CoW fork; this partially takes care of (1) but extent-size reservations
+ * will have to periodically relog even if there's no writeout in progress.
+ * This can happen if the CoW extent size hint is set, which you really want.
+ * Third, EFIs cannot currently be automatically relogged into newer
+ * transactions to advance the log tail.  Fourth, stuffing the log full of
+ * EFIs places an upper bound on the number of CoW allocations that can be
+ * held filesystem-wide at any given time.  Recording them in the refcount
+ * btree doesn't require us to maintain any state in memory and doesn't pin
+ * the log.
+ */
+/*
+ * Adjust the refcounts of CoW allocations.  These allocations are "magic"
+ * in that they're not referenced anywhere else in the filesystem, so we
+ * stash them in the refcount btree with a refcount of 1 until either file
+ * remapping (or CoW cancellation) happens.
+ */
+STATIC int
+xfs_refcount_adjust_cow_extents(
+	struct xfs_btree_cur	*cur,
+	xfs_agblock_t		agbno,
+	xfs_extlen_t		aglen,
+	enum xfs_refc_adjust_op	adj,
+	struct xfs_defer_ops	*dfops,
+	struct xfs_owner_info	*oinfo)
+{
+	struct xfs_refcount_irec	ext, tmp;
+	int				error;
+	int				found_rec, found_tmp;
+
+	if (aglen == 0)
+		return 0;
+
+	/* Find any overlapping refcount records */
+	error = xfs_refcount_lookup_ge(cur, agbno, &found_rec);
+	if (error)
+		goto out_error;
+	error = xfs_refcount_get_rec(cur, &ext, &found_rec);
+	if (error)
+		goto out_error;
+	if (!found_rec) {
+		ext.rc_startblock = cur->bc_mp->m_sb.sb_agblocks +
+				XFS_REFC_COW_START;
+		ext.rc_blockcount = 0;
+		ext.rc_refcount = 0;
+	}
+
+	switch (adj) {
+	case XFS_REFCOUNT_ADJUST_COW_ALLOC:
+		/* Adding a CoW reservation, there should be nothing here. */
+		XFS_WANT_CORRUPTED_GOTO(cur->bc_mp,
+				ext.rc_startblock >= agbno + aglen, out_error);
+
+		tmp.rc_startblock = agbno;
+		tmp.rc_blockcount = aglen;
+		tmp.rc_refcount = 1;
+		trace_xfs_refcount_modify_extent(cur->bc_mp,
+				cur->bc_private.a.agno, &tmp);
+
+		error = xfs_refcount_insert(cur, &tmp,
+				&found_tmp);
+		if (error)
+			goto out_error;
+		XFS_WANT_CORRUPTED_GOTO(cur->bc_mp,
+				found_tmp == 1, out_error);
+		break;
+	case XFS_REFCOUNT_ADJUST_COW_FREE:
+		/* Removing a CoW reservation, there should be one extent. */
+		XFS_WANT_CORRUPTED_GOTO(cur->bc_mp,
+			ext.rc_startblock == agbno, out_error);
+		XFS_WANT_CORRUPTED_GOTO(cur->bc_mp,
+			ext.rc_blockcount == aglen, out_error);
+		XFS_WANT_CORRUPTED_GOTO(cur->bc_mp,
+			ext.rc_refcount == 1, out_error);
+
+		ext.rc_refcount = 0;
+		trace_xfs_refcount_modify_extent(cur->bc_mp,
+				cur->bc_private.a.agno, &ext);
+		error = xfs_refcount_delete(cur, &found_rec);
+		if (error)
+			goto out_error;
+		XFS_WANT_CORRUPTED_GOTO(cur->bc_mp,
+				found_rec == 1, out_error);
+		break;
+	default:
+		ASSERT(0);
+	}
+
+	return error;
+out_error:
+	trace_xfs_refcount_modify_extent_error(cur->bc_mp,
+			cur->bc_private.a.agno, error, _RET_IP_);
+	return error;
+}
+
+/*
+ * Add or remove refcount btree entries for CoW reservations.
+ */
+STATIC int
+xfs_refcount_adjust_cow(
+	struct xfs_btree_cur	*cur,
+	xfs_agblock_t		agbno,
+	xfs_extlen_t		aglen,
+	enum xfs_refc_adjust_op	adj,
+	struct xfs_defer_ops	*dfops)
+{
+	bool			shape_changed;
+	int			error;
+
+	agbno += XFS_REFC_COW_START;
+
+	/*
+	 * Ensure that no rcextents cross the boundary of the adjustment range.
+	 */
+	error = xfs_refcount_split_extent(cur, agbno, &shape_changed);
+	if (error)
+		goto out_error;
+
+	error = xfs_refcount_split_extent(cur, agbno + aglen, &shape_changed);
+	if (error)
+		goto out_error;
+
+	/*
+	 * Try to merge with the left or right extents of the range.
+	 */
+	error = xfs_refcount_merge_extents(cur, &agbno, &aglen, adj,
+			XFS_FIND_RCEXT_COW, &shape_changed);
+	if (error)
+		goto out_error;
+
+	/* Now that we've taken care of the ends, adjust the middle extents */
+	error = xfs_refcount_adjust_cow_extents(cur, agbno, aglen, adj,
+			dfops, NULL);
+	if (error)
+		goto out_error;
+
+	return 0;
+
+out_error:
+	trace_xfs_refcount_adjust_cow_error(cur->bc_mp, cur->bc_private.a.agno,
+			error, _RET_IP_);
+	return error;
+}
+
+/*
+ * Record a CoW allocation in the refcount btree.
+ */
+STATIC int
+__xfs_refcount_cow_alloc(
+	struct xfs_btree_cur	*rcur,
+	xfs_agblock_t		agbno,
+	xfs_extlen_t		aglen,
+	struct xfs_defer_ops	*dfops)
+{
+	int			error;
+
+	trace_xfs_refcount_cow_increase(rcur->bc_mp, rcur->bc_private.a.agno,
+			agbno, aglen);
+
+	/* Add refcount btree reservation */
+	error = xfs_refcount_adjust_cow(rcur, agbno, aglen,
+			XFS_REFCOUNT_ADJUST_COW_ALLOC, dfops);
+	if (error)
+		return error;
+
+	/* Add rmap entry */
+	if (xfs_sb_version_hasrmapbt(&rcur->bc_mp->m_sb)) {
+		error = xfs_rmap_alloc_extent(rcur->bc_mp, dfops,
+				rcur->bc_private.a.agno,
+				agbno, aglen, XFS_RMAP_OWN_COW);
+		if (error)
+			return error;
+	}
+
+	return error;
+}
+
+/*
+ * Remove a CoW allocation from the refcount btree.
+ */
+STATIC int
+__xfs_refcount_cow_free(
+	struct xfs_btree_cur	*rcur,
+	xfs_agblock_t		agbno,
+	xfs_extlen_t		aglen,
+	struct xfs_defer_ops	*dfops)
+{
+	int			error;
+
+	trace_xfs_refcount_cow_decrease(rcur->bc_mp, rcur->bc_private.a.agno,
+			agbno, aglen);
+
+	/* Remove refcount btree reservation */
+	error = xfs_refcount_adjust_cow(rcur, agbno, aglen,
+			XFS_REFCOUNT_ADJUST_COW_FREE, dfops);
+	if (error)
+		return error;
+
+	/* Remove rmap entry */
+	if (xfs_sb_version_hasrmapbt(&rcur->bc_mp->m_sb)) {
+		error = xfs_rmap_free_extent(rcur->bc_mp, dfops,
+				rcur->bc_private.a.agno,
+				agbno, aglen, XFS_RMAP_OWN_COW);
+		if (error)
+			return error;
+	}
+
+	return error;
+}
+
+/* Record a CoW staging extent in the refcount btree. */
+int
+xfs_refcount_alloc_cow_extent(
+	struct xfs_mount		*mp,
+	struct xfs_defer_ops		*dfops,
+	xfs_fsblock_t			fsb,
+	xfs_extlen_t			len)
+{
+	if (!xfs_sb_version_hasreflink(&mp->m_sb))
+		return 0;
+
+	return __xfs_refcount_add(mp, dfops, XFS_REFCOUNT_ALLOC_COW,
+			fsb, len);
+}
+
+/* Forget a CoW staging event in the refcount btree. */
+int
+xfs_refcount_free_cow_extent(
+	struct xfs_mount		*mp,
+	struct xfs_defer_ops		*dfops,
+	xfs_fsblock_t			fsb,
+	xfs_extlen_t			len)
+{
+	if (!xfs_sb_version_hasreflink(&mp->m_sb))
+		return 0;
+
+	return __xfs_refcount_add(mp, dfops, XFS_REFCOUNT_FREE_COW,
+			fsb, len);
+}
+
+struct xfs_refcount_recovery {
+	struct list_head		rr_list;
+	struct xfs_refcount_irec	rr_rrec;
+};
+
+/* Stuff an extent on the recovery list. */
+STATIC int
+xfs_refcount_recover_extent(
+	struct xfs_btree_cur		*cur,
+	union xfs_btree_rec		*rec,
+	void				*priv)
+{
+	struct list_head		*debris = priv;
+	struct xfs_refcount_recovery	*rr;
+
+	if (be32_to_cpu(rec->refc.rc_refcount) != 1)
+		return -EFSCORRUPTED;
+
+	rr = kmem_alloc(sizeof(struct xfs_refcount_recovery), KM_SLEEP);
+	xfs_refcount_btrec_to_irec(rec, &rr->rr_rrec);
+	list_add_tail(&rr->rr_list, debris);
+
+	return 0;
+}
+
+/* Find and remove leftover CoW reservations. */
+int
+xfs_refcount_recover_cow_leftovers(
+	struct xfs_mount		*mp,
+	xfs_agnumber_t			agno)
+{
+	struct xfs_trans		*tp;
+	struct xfs_btree_cur		*cur;
+	struct xfs_buf			*agbp;
+	struct xfs_refcount_recovery	*rr, *n;
+	struct list_head		debris;
+	union xfs_btree_irec		low;
+	union xfs_btree_irec		high;
+	struct xfs_defer_ops		dfops;
+	xfs_fsblock_t			fsb;
+	xfs_agblock_t			agbno;
+	int				error;
+
+	if (mp->m_sb.sb_agblocks >= XFS_REFC_COW_START)
+		return -EOPNOTSUPP;
+
+	error = xfs_alloc_read_agf(mp, NULL, agno, 0, &agbp);
+	if (error)
+		return error;
+	cur = xfs_refcountbt_init_cursor(mp, NULL, agbp, agno, NULL);
+
+	/* Find all the leftover CoW staging extents. */
+	INIT_LIST_HEAD(&debris);
+	memset(&low, 0, sizeof(low));
+	memset(&high, 0, sizeof(high));
+	low.rc.rc_startblock = XFS_REFC_COW_START;
+	high.rc.rc_startblock = -1U;
+	error = xfs_btree_query_range(cur, &low, &high,
+			xfs_refcount_recover_extent, &debris);
+	if (error)
+		goto out_error;
+	xfs_btree_del_cursor(cur, XFS_BTREE_NOERROR);
+	xfs_buf_relse(agbp);
+
+	/* Now iterate the list to free the leftovers */
+	list_for_each_entry(rr, &debris, rr_list) {
+		/* Set up transaction. */
+		error = xfs_trans_alloc(mp, &M_RES(mp)->tr_write, 0, 0, 0, &tp);
+		if (error)
+			goto out_free;
+
+		trace_xfs_refcount_recover_extent(mp, agno, &rr->rr_rrec);
+
+		/* Free the orphan record */
+		xfs_defer_init(&dfops, &fsb);
+		agbno = rr->rr_rrec.rc_startblock - XFS_REFC_COW_START;
+		fsb = XFS_AGB_TO_FSB(mp, agno, agbno);
+		error = xfs_refcount_free_cow_extent(mp, &dfops, fsb,
+				rr->rr_rrec.rc_blockcount);
+		if (error)
+			goto out_defer;
+
+		/* Free the block. */
+		xfs_bmap_add_free(mp, &dfops, fsb,
+				rr->rr_rrec.rc_blockcount, NULL);
+
+		error = xfs_defer_finish(&tp, &dfops, NULL);
+		if (error)
+			goto out_defer;
+
+		error = xfs_trans_commit(tp);
+		if (error)
+			goto out_cancel;
+	}
+	goto out_free;
+
+out_defer:
+	xfs_defer_cancel(&dfops);
+out_cancel:
+	xfs_trans_cancel(tp);
+
+out_free:
+	/* Free the leftover list */
+	list_for_each_entry_safe(rr, n, &debris, rr_list) {
+		list_del(&rr->rr_list);
+		kmem_free(rr);
+	}
+
+	return error;
+
+out_error:
+	xfs_btree_del_cursor(cur, XFS_BTREE_ERROR);
+	xfs_buf_relse(agbp);
+	return error;
+}
diff --git a/fs/xfs/libxfs/xfs_refcount.h b/fs/xfs/libxfs/xfs_refcount.h
index adba3ae2b55f..098dc668ab2c 100644
--- a/fs/xfs/libxfs/xfs_refcount.h
+++ b/fs/xfs/libxfs/xfs_refcount.h
@@ -58,4 +58,13 @@ extern int xfs_refcount_find_shared(struct xfs_btree_cur *cur,
 		xfs_agblock_t agbno, xfs_extlen_t aglen, xfs_agblock_t *fbno,
 		xfs_extlen_t *flen, bool find_end_of_shared);
 
+extern int xfs_refcount_alloc_cow_extent(struct xfs_mount *mp,
+		struct xfs_defer_ops *dfops, xfs_fsblock_t fsb,
+		xfs_extlen_t len);
+extern int xfs_refcount_free_cow_extent(struct xfs_mount *mp,
+		struct xfs_defer_ops *dfops, xfs_fsblock_t fsb,
+		xfs_extlen_t len);
+extern int xfs_refcount_recover_cow_leftovers(struct xfs_mount *mp,
+		xfs_agnumber_t agno);
+
 #endif	/* __XFS_REFCOUNT_H__ */
diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
index a78a1164bab3..099c00ecb078 100644
--- a/fs/xfs/xfs_mount.c
+++ b/fs/xfs/xfs_mount.c
@@ -44,6 +44,7 @@
 #include "xfs_sysfs.h"
 #include "xfs_rmap_btree.h"
 #include "xfs_refcount_btree.h"
+#include "xfs_reflink.h"
 
 
 static DEFINE_MUTEX(xfs_uuid_table_mutex);
@@ -985,10 +986,21 @@ xfs_mountfs(
 		if (error)
 			xfs_warn(mp,
 	"Unable to allocate reserve blocks. Continuing without reserve pool.");
+
+		/* Recover any CoW blocks that never got remapped. */
+		error = xfs_reflink_recover_cow(mp);
+		if (error) {
+			xfs_err(mp,
+	"Error %d recovering leftover CoW allocations.", error);
+			xfs_force_shutdown(mp, SHUTDOWN_CORRUPT_INCORE);
+			goto out_quota;
+		}
 	}
 
 	return 0;
 
+ out_quota:
+	xfs_qm_unmount_quotas(mp);
  out_rtunmount:
 	xfs_rtunmount_inodes(mp);
  out_rele_rip:
diff --git a/fs/xfs/xfs_refcount_item.c b/fs/xfs/xfs_refcount_item.c
index 82153e2a057c..fe86a668a57e 100644
--- a/fs/xfs/xfs_refcount_item.c
+++ b/fs/xfs/xfs_refcount_item.c
@@ -502,6 +502,18 @@ xfs_cui_recover(
 				error = xfs_refcount_decrease_extent(
 						tp->t_mountp, &dfops, &irec);
 				break;
+			case XFS_REFCOUNT_ALLOC_COW:
+				error = xfs_refcount_alloc_cow_extent(
+						tp->t_mountp, &dfops,
+						irec.br_startblock,
+						irec.br_blockcount);
+				break;
+			case XFS_REFCOUNT_FREE_COW:
+				error = xfs_refcount_free_cow_extent(
+						tp->t_mountp, &dfops,
+						irec.br_startblock,
+						irec.br_blockcount);
+				break;
 			default:
 				ASSERT(0);
 			}
diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
index a30be03395fb..0aac26208a82 100644
--- a/fs/xfs/xfs_reflink.c
+++ b/fs/xfs/xfs_reflink.c
@@ -40,6 +40,7 @@
 #include "xfs_log.h"
 #include "xfs_icache.h"
 #include "xfs_pnfs.h"
+#include "xfs_btree.h"
 #include "xfs_refcount_btree.h"
 #include "xfs_refcount.h"
 #include "xfs_bmap_btree.h"
@@ -563,6 +564,13 @@ xfs_reflink_cancel_cow_blocks(
 			xfs_trans_ijoin(*tpp, ip, 0);
 			xfs_defer_init(&dfops, &firstfsb);
 
+			/* Free the CoW orphan record. */
+			error = xfs_refcount_free_cow_extent(ip->i_mount,
+					&dfops, irec.br_startblock,
+					irec.br_blockcount);
+			if (error)
+				break;
+
 			xfs_bmap_add_free(ip->i_mount, &dfops,
 					irec.br_startblock, irec.br_blockcount,
 					NULL);
@@ -719,6 +727,13 @@ xfs_reflink_end_cow(
 			irec.br_blockcount = rlen;
 			trace_xfs_reflink_cow_remap_piece(ip, &uirec);
 
+			/* Free the CoW orphan record. */
+			error = xfs_refcount_free_cow_extent(tp->t_mountp,
+					&dfops, uirec.br_startblock,
+					uirec.br_blockcount);
+			if (error)
+				goto out_defer;
+
 			/* Map the new blocks into the data fork. */
 			error = xfs_bmap_map_extent(tp->t_mountp, &dfops,
 					ip, &uirec);
@@ -755,3 +770,25 @@ out:
 	trace_xfs_reflink_end_cow_error(ip, error, _RET_IP_);
 	return error;
 }
+
+/*
+ * Free leftover CoW reservations that didn't get cleaned out.
+ */
+int
+xfs_reflink_recover_cow(
+	struct xfs_mount	*mp)
+{
+	xfs_agnumber_t		agno;
+	int			error = 0;
+
+	if (!xfs_sb_version_hasreflink(&mp->m_sb))
+		return 0;
+
+	for (agno = 0; agno < mp->m_sb.sb_agcount; agno++) {
+		error = xfs_refcount_recover_cow_leftovers(mp, agno);
+		if (error)
+			break;
+	}
+
+	return error;
+}
diff --git a/fs/xfs/xfs_reflink.h b/fs/xfs/xfs_reflink.h
index c0c989ae84bc..1d2f180f9eca 100644
--- a/fs/xfs/xfs_reflink.h
+++ b/fs/xfs/xfs_reflink.h
@@ -42,5 +42,6 @@ extern int xfs_reflink_cancel_cow_range(struct xfs_inode *ip, xfs_off_t offset,
 		xfs_off_t count);
 extern int xfs_reflink_end_cow(struct xfs_inode *ip, xfs_off_t offset,
 		xfs_off_t count);
+extern int xfs_reflink_recover_cow(struct xfs_mount *mp);
 
 #endif /* __XFS_REFLINK_H */
diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index b65b97997f99..c32e7e61e7f3 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -1316,6 +1316,15 @@ xfs_fs_remount(
 		xfs_restore_resvblks(mp);
 		xfs_log_work_queue(mp);
 		xfs_queue_eofblocks(mp);
+
+		/* Recover any CoW blocks that never got remapped. */
+		error = xfs_reflink_recover_cow(mp);
+		if (error) {
+			xfs_err(mp,
+	"Error %d recovering leftover CoW allocations.", error);
+			xfs_force_shutdown(mp, SHUTDOWN_CORRUPT_INCORE);
+			return error;
+		}
 	}
 
 	/* rw -> ro */
diff --git a/fs/xfs/xfs_trace.h b/fs/xfs/xfs_trace.h
index 6a9ae9eaec7f..5c10b12170d0 100644
--- a/fs/xfs/xfs_trace.h
+++ b/fs/xfs/xfs_trace.h
@@ -2916,14 +2916,18 @@ DEFINE_AG_ERROR_EVENT(xfs_refcount_update_error);
 /* refcount adjustment tracepoints */
 DEFINE_AG_EXTENT_EVENT(xfs_refcount_increase);
 DEFINE_AG_EXTENT_EVENT(xfs_refcount_decrease);
+DEFINE_AG_EXTENT_EVENT(xfs_refcount_cow_increase);
+DEFINE_AG_EXTENT_EVENT(xfs_refcount_cow_decrease);
 DEFINE_REFCOUNT_TRIPLE_EXTENT_EVENT(xfs_refcount_merge_center_extents);
 DEFINE_REFCOUNT_EXTENT_EVENT(xfs_refcount_modify_extent);
+DEFINE_REFCOUNT_EXTENT_EVENT(xfs_refcount_recover_extent);
 DEFINE_REFCOUNT_EXTENT_AT_EVENT(xfs_refcount_split_extent);
 DEFINE_REFCOUNT_DOUBLE_EXTENT_EVENT(xfs_refcount_merge_left_extent);
 DEFINE_REFCOUNT_DOUBLE_EXTENT_EVENT(xfs_refcount_merge_right_extent);
 DEFINE_REFCOUNT_DOUBLE_EXTENT_AT_EVENT(xfs_refcount_find_left_extent);
 DEFINE_REFCOUNT_DOUBLE_EXTENT_AT_EVENT(xfs_refcount_find_right_extent);
 DEFINE_AG_ERROR_EVENT(xfs_refcount_adjust_error);
+DEFINE_AG_ERROR_EVENT(xfs_refcount_adjust_cow_error);
 DEFINE_AG_ERROR_EVENT(xfs_refcount_merge_center_extents_error);
 DEFINE_AG_ERROR_EVENT(xfs_refcount_modify_extent_error);
 DEFINE_AG_ERROR_EVENT(xfs_refcount_split_extent_error);