xfs: adjust refcount of an extent of blocks in refcount btree

Provide functions to adjust the reference counts for an extent of
physical blocks stored in the refcount btree.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

2 files changed, 817 insertions, 1 deletions

diff --git a/fs/xfs/libxfs/xfs_refcount.c b/fs/xfs/libxfs/xfs_refcount.c
index de1340652933..f522fe130a16 100644
--- a/fs/xfs/libxfs/xfs_refcount.c
+++ b/fs/xfs/libxfs/xfs_refcount.c
@@ -37,6 +37,12 @@
 #include "xfs_bit.h"
 #include "xfs_refcount.h"
 
+/* Allowable refcount adjustment amounts. */
+enum xfs_refc_adjust_op {
+        XFS_REFCOUNT_ADJUST_INCREASE    = 1,
+        XFS_REFCOUNT_ADJUST_DECREASE    = -1,
+};
+
 /*
  * Look up the first record less than or equal to [bno, len] in the btree
  * given by cur.
@@ -175,3 +181,811 @@ out_error:
                                 cur->bc_private.a.agno, error, _RET_IP_);
         return error;
 }
+
+/*
+ * Adjusting the Reference Count
+ *
+ * As stated elsewhere, the reference count btree (refcbt) stores
+ * >1 reference counts for extents of physical blocks.  In this
+ * operation, we're either raising or lowering the reference count of
+ * some subrange stored in the tree:
+ *
+ *      <------ adjustment range ------>
+ * ----+   +---+-----+ +--+--------+---------
+ *  2  |   | 3 |  4  | |17|   55   |   10
+ * ----+   +---+-----+ +--+--------+---------
+ * X axis is physical blocks number;
+ * reference counts are the numbers inside the rectangles
+ *
+ * The first thing we need to do is to ensure that there are no
+ * refcount extents crossing either boundary of the range to be
+ * adjusted.  For any extent that does cross a boundary, split it into
+ * two extents so that we can increment the refcount of one of the
+ * pieces later:
+ *
+ *      <------ adjustment range ------>
+ * ----+   +---+-----+ +--+--------+----+----
+ *  2  |   | 3 |  2  | |17|   55   | 10 | 10
+ * ----+   +---+-----+ +--+--------+----+----
+ *
+ * For this next step, let's assume that all the physical blocks in
+ * the adjustment range are mapped to a file and are therefore in use
+ * at least once.  Therefore, we can infer that any gap in the
+ * refcount tree within the adjustment range represents a physical
+ * extent with refcount == 1:
+ *
+ *      <------ adjustment range ------>
+ * ----+---+---+-----+-+--+--------+----+----
+ *  2  |"1"| 3 |  2  |1|17|   55   | 10 | 10
+ * ----+---+---+-----+-+--+--------+----+----
+ *      ^
+ *
+ * For each extent that falls within the interval range, figure out
+ * which extent is to the left or the right of that extent.  Now we
+ * have a left, current, and right extent.  If the new reference count
+ * of the center extent enables us to merge left, center, and right
+ * into one record covering all three, do so.  If the center extent is
+ * at the left end of the range, abuts the left extent, and its new
+ * reference count matches the left extent's record, then merge them.
+ * If the center extent is at the right end of the range, abuts the
+ * right extent, and the reference counts match, merge those.  In the
+ * example, we can left merge (assuming an increment operation):
+ *
+ *      <------ adjustment range ------>
+ * --------+---+-----+-+--+--------+----+----
+ *    2    | 3 |  2  |1|17|   55   | 10 | 10
+ * --------+---+-----+-+--+--------+----+----
+ *          ^
+ *
+ * For all other extents within the range, adjust the reference count
+ * or delete it if the refcount falls below 2.  If we were
+ * incrementing, the end result looks like this:
+ *
+ *      <------ adjustment range ------>
+ * --------+---+-----+-+--+--------+----+----
+ *    2    | 4 |  3  |2|18|   56   | 11 | 10
+ * --------+---+-----+-+--+--------+----+----
+ *
+ * The result of a decrement operation looks as such:
+ *
+ *      <------ adjustment range ------>
+ * ----+   +---+       +--+--------+----+----
+ *  2  |   | 2 |       |16|   54   |  9 | 10
+ * ----+   +---+       +--+--------+----+----
+ *      DDDD    111111DD
+ *
+ * The blocks marked "D" are freed; the blocks marked "1" are only
+ * referenced once and therefore the record is removed from the
+ * refcount btree.
+ */
+
+/* Next block after this extent. */
+static inline xfs_agblock_t
+xfs_refc_next(
+        struct xfs_refcount_irec        *rc)
+{
+        return rc->rc_startblock + rc->rc_blockcount;
+}
+
+/*
+ * Split a refcount extent that crosses agbno.
+ */
+STATIC int
+xfs_refcount_split_extent(
+        struct xfs_btree_cur            *cur,
+        xfs_agblock_t                   agbno,
+        bool                            *shape_changed)
+{
+        struct xfs_refcount_irec        rcext, tmp;
+        int                             found_rec;
+        int                             error;
+
+        *shape_changed = false;
+        error = xfs_refcount_lookup_le(cur, agbno, &found_rec);
+        if (error)
+                goto out_error;
+        if (!found_rec)
+                return 0;
+
+        error = xfs_refcount_get_rec(cur, &rcext, &found_rec);
+        if (error)
+                goto out_error;
+        XFS_WANT_CORRUPTED_GOTO(cur->bc_mp, found_rec == 1, out_error);
+        if (rcext.rc_startblock == agbno || xfs_refc_next(&rcext) <= agbno)
+                return 0;
+
+        *shape_changed = true;
+        trace_xfs_refcount_split_extent(cur->bc_mp, cur->bc_private.a.agno,
+                        &rcext, agbno);
+
+        /* Establish the right extent. */
+        tmp = rcext;
+        tmp.rc_startblock = agbno;
+        tmp.rc_blockcount -= (agbno - rcext.rc_startblock);
+        error = xfs_refcount_update(cur, &tmp);
+        if (error)
+                goto out_error;
+
+        /* Insert the left extent. */
+        tmp = rcext;
+        tmp.rc_blockcount = agbno - rcext.rc_startblock;
+        error = xfs_refcount_insert(cur, &tmp, &found_rec);
+        if (error)
+                goto out_error;
+        XFS_WANT_CORRUPTED_GOTO(cur->bc_mp, found_rec == 1, out_error);
+        return error;
+
+out_error:
+        trace_xfs_refcount_split_extent_error(cur->bc_mp,
+                        cur->bc_private.a.agno, error, _RET_IP_);
+        return error;
+}
+
+/*
+ * Merge the left, center, and right extents.
+ */
+STATIC int
+xfs_refcount_merge_center_extents(
+        struct xfs_btree_cur            *cur,
+        struct xfs_refcount_irec        *left,
+        struct xfs_refcount_irec        *center,
+        struct xfs_refcount_irec        *right,
+        unsigned long long              extlen,
+        xfs_agblock_t                   *agbno,
+        xfs_extlen_t                    *aglen)
+{
+        int                             error;
+        int                             found_rec;
+
+        trace_xfs_refcount_merge_center_extents(cur->bc_mp,
+                        cur->bc_private.a.agno, left, center, right);
+
+        /*
+         * Make sure the center and right extents are not in the btree.
+         * If the center extent was synthesized, the first delete call
+         * removes the right extent and we skip the second deletion.
+         * If center and right were in the btree, then the first delete
+         * call removes the center and the second one removes the right
+         * extent.
+         */
+        error = xfs_refcount_lookup_ge(cur, center->rc_startblock,
+                        &found_rec);
+        if (error)
+                goto out_error;
+        XFS_WANT_CORRUPTED_GOTO(cur->bc_mp, found_rec == 1, out_error);
+
+        error = xfs_refcount_delete(cur, &found_rec);
+        if (error)
+                goto out_error;
+        XFS_WANT_CORRUPTED_GOTO(cur->bc_mp, found_rec == 1, out_error);
+
+        if (center->rc_refcount > 1) {
+                error = xfs_refcount_delete(cur, &found_rec);
+                if (error)
+                        goto out_error;
+                XFS_WANT_CORRUPTED_GOTO(cur->bc_mp, found_rec == 1,
+                                out_error);
+        }
+
+        /* Enlarge the left extent. */
+        error = xfs_refcount_lookup_le(cur, left->rc_startblock,
+                        &found_rec);
+        if (error)
+                goto out_error;
+        XFS_WANT_CORRUPTED_GOTO(cur->bc_mp, found_rec == 1, out_error);
+
+        left->rc_blockcount = extlen;
+        error = xfs_refcount_update(cur, left);
+        if (error)
+                goto out_error;
+
+        *aglen = 0;
+        return error;
+
+out_error:
+        trace_xfs_refcount_merge_center_extents_error(cur->bc_mp,
+                        cur->bc_private.a.agno, error, _RET_IP_);
+        return error;
+}
+
+/*
+ * Merge with the left extent.
+ */
+STATIC int
+xfs_refcount_merge_left_extent(
+        struct xfs_btree_cur            *cur,
+        struct xfs_refcount_irec        *left,
+        struct xfs_refcount_irec        *cleft,
+        xfs_agblock_t                   *agbno,
+        xfs_extlen_t                    *aglen)
+{
+        int                             error;
+        int                             found_rec;
+
+        trace_xfs_refcount_merge_left_extent(cur->bc_mp,
+                        cur->bc_private.a.agno, left, cleft);
+
+        /* If the extent at agbno (cleft) wasn't synthesized, remove it. */
+        if (cleft->rc_refcount > 1) {
+                error = xfs_refcount_lookup_le(cur, cleft->rc_startblock,
+                                &found_rec);
+                if (error)
+                        goto out_error;
+                XFS_WANT_CORRUPTED_GOTO(cur->bc_mp, found_rec == 1,
+                                out_error);
+
+                error = xfs_refcount_delete(cur, &found_rec);
+                if (error)
+                        goto out_error;
+                XFS_WANT_CORRUPTED_GOTO(cur->bc_mp, found_rec == 1,
+                                out_error);
+        }
+
+        /* Enlarge the left extent. */
+        error = xfs_refcount_lookup_le(cur, left->rc_startblock,
+                        &found_rec);
+        if (error)
+                goto out_error;
+        XFS_WANT_CORRUPTED_GOTO(cur->bc_mp, found_rec == 1, out_error);
+
+        left->rc_blockcount += cleft->rc_blockcount;
+        error = xfs_refcount_update(cur, left);
+        if (error)
+                goto out_error;
+
+        *agbno += cleft->rc_blockcount;
+        *aglen -= cleft->rc_blockcount;
+        return error;
+
+out_error:
+        trace_xfs_refcount_merge_left_extent_error(cur->bc_mp,
+                        cur->bc_private.a.agno, error, _RET_IP_);
+        return error;
+}
+
+/*
+ * Merge with the right extent.
+ */
+STATIC int
+xfs_refcount_merge_right_extent(
+        struct xfs_btree_cur            *cur,
+        struct xfs_refcount_irec        *right,
+        struct xfs_refcount_irec        *cright,
+        xfs_agblock_t                   *agbno,
+        xfs_extlen_t                    *aglen)
+{
+        int                             error;
+        int                             found_rec;
+
+        trace_xfs_refcount_merge_right_extent(cur->bc_mp,
+                        cur->bc_private.a.agno, cright, right);
+
+        /*
+         * If the extent ending at agbno+aglen (cright) wasn't synthesized,
+         * remove it.
+         */
+        if (cright->rc_refcount > 1) {
+                error = xfs_refcount_lookup_le(cur, cright->rc_startblock,
+                        &found_rec);
+                if (error)
+                        goto out_error;
+                XFS_WANT_CORRUPTED_GOTO(cur->bc_mp, found_rec == 1,
+                                out_error);
+
+                error = xfs_refcount_delete(cur, &found_rec);
+                if (error)
+                        goto out_error;
+                XFS_WANT_CORRUPTED_GOTO(cur->bc_mp, found_rec == 1,
+                                out_error);
+        }
+
+        /* Enlarge the right extent. */
+        error = xfs_refcount_lookup_le(cur, right->rc_startblock,
+                        &found_rec);
+        if (error)
+                goto out_error;
+        XFS_WANT_CORRUPTED_GOTO(cur->bc_mp, found_rec == 1, out_error);
+
+        right->rc_startblock -= cright->rc_blockcount;
+        right->rc_blockcount += cright->rc_blockcount;
+        error = xfs_refcount_update(cur, right);
+        if (error)
+                goto out_error;
+
+        *aglen -= cright->rc_blockcount;
+        return error;
+
+out_error:
+        trace_xfs_refcount_merge_right_extent_error(cur->bc_mp,
+                        cur->bc_private.a.agno, error, _RET_IP_);
+        return error;
+}
+
+/*
+ * Find the left extent and the one after it (cleft).  This function assumes
+ * that we've already split any extent crossing agbno.
+ */
+STATIC int
+xfs_refcount_find_left_extents(
+        struct xfs_btree_cur            *cur,
+        struct xfs_refcount_irec        *left,
+        struct xfs_refcount_irec        *cleft,
+        xfs_agblock_t                   agbno,
+        xfs_extlen_t                    aglen)
+{
+        struct xfs_refcount_irec        tmp;
+        int                             error;
+        int                             found_rec;
+
+        left->rc_startblock = cleft->rc_startblock = NULLAGBLOCK;
+        error = xfs_refcount_lookup_le(cur, agbno - 1, &found_rec);
+        if (error)
+                goto out_error;
+        if (!found_rec)
+                return 0;
+
+        error = xfs_refcount_get_rec(cur, &tmp, &found_rec);
+        if (error)
+                goto out_error;
+        XFS_WANT_CORRUPTED_GOTO(cur->bc_mp, found_rec == 1, out_error);
+
+        if (xfs_refc_next(&tmp) != agbno)
+                return 0;
+        /* We have a left extent; retrieve (or invent) the next right one */
+        *left = tmp;
+
+        error = xfs_btree_increment(cur, 0, &found_rec);
+        if (error)
+                goto out_error;
+        if (found_rec) {
+                error = xfs_refcount_get_rec(cur, &tmp, &found_rec);
+                if (error)
+                        goto out_error;
+                XFS_WANT_CORRUPTED_GOTO(cur->bc_mp, found_rec == 1,
+                                out_error);
+
+                /* if tmp starts at the end of our range, just use that */
+                if (tmp.rc_startblock == agbno)
+                        *cleft = tmp;
+                else {
+                        /*
+                         * There's a gap in the refcntbt at the start of the
+                         * range we're interested in (refcount == 1) so
+                         * synthesize the implied extent and pass it back.
+                         * We assume here that the agbno/aglen range was
+                         * passed in from a data fork extent mapping and
+                         * therefore is allocated to exactly one owner.
+                         */
+                        cleft->rc_startblock = agbno;
+                        cleft->rc_blockcount = min(aglen,
+                                        tmp.rc_startblock - agbno);
+                        cleft->rc_refcount = 1;
+                }
+        } else {
+                /*
+                 * No extents, so pretend that there's one covering the whole
+                 * range.
+                 */
+                cleft->rc_startblock = agbno;
+                cleft->rc_blockcount = aglen;
+                cleft->rc_refcount = 1;
+        }
+        trace_xfs_refcount_find_left_extent(cur->bc_mp, cur->bc_private.a.agno,
+                        left, cleft, agbno);
+        return error;
+
+out_error:
+        trace_xfs_refcount_find_left_extent_error(cur->bc_mp,
+                        cur->bc_private.a.agno, error, _RET_IP_);
+        return error;
+}
+
+/*
+ * Find the right extent and the one before it (cright).  This function
+ * assumes that we've already split any extents crossing agbno + aglen.
+ */
+STATIC int
+xfs_refcount_find_right_extents(
+        struct xfs_btree_cur            *cur,
+        struct xfs_refcount_irec        *right,
+        struct xfs_refcount_irec        *cright,
+        xfs_agblock_t                   agbno,
+        xfs_extlen_t                    aglen)
+{
+        struct xfs_refcount_irec        tmp;
+        int                             error;
+        int                             found_rec;
+
+        right->rc_startblock = cright->rc_startblock = NULLAGBLOCK;
+        error = xfs_refcount_lookup_ge(cur, agbno + aglen, &found_rec);
+        if (error)
+                goto out_error;
+        if (!found_rec)
+                return 0;
+
+        error = xfs_refcount_get_rec(cur, &tmp, &found_rec);
+        if (error)
+                goto out_error;
+        XFS_WANT_CORRUPTED_GOTO(cur->bc_mp, found_rec == 1, out_error);
+
+        if (tmp.rc_startblock != agbno + aglen)
+                return 0;
+        /* We have a right extent; retrieve (or invent) the next left one */
+        *right = tmp;
+
+        error = xfs_btree_decrement(cur, 0, &found_rec);
+        if (error)
+                goto out_error;
+        if (found_rec) {
+                error = xfs_refcount_get_rec(cur, &tmp, &found_rec);
+                if (error)
+                        goto out_error;
+                XFS_WANT_CORRUPTED_GOTO(cur->bc_mp, found_rec == 1,
+                                out_error);
+
+                /* if tmp ends at the end of our range, just use that */
+                if (xfs_refc_next(&tmp) == agbno + aglen)
+                        *cright = tmp;
+                else {
+                        /*
+                         * There's a gap in the refcntbt at the end of the
+                         * range we're interested in (refcount == 1) so
+                         * create the implied extent and pass it back.
+                         * We assume here that the agbno/aglen range was
+                         * passed in from a data fork extent mapping and
+                         * therefore is allocated to exactly one owner.
+                         */
+                        cright->rc_startblock = max(agbno, xfs_refc_next(&tmp));
+                        cright->rc_blockcount = right->rc_startblock -
+                                        cright->rc_startblock;
+                        cright->rc_refcount = 1;
+                }
+        } else {
+                /*
+                 * No extents, so pretend that there's one covering the whole
+                 * range.
+                 */
+                cright->rc_startblock = agbno;
+                cright->rc_blockcount = aglen;
+                cright->rc_refcount = 1;
+        }
+        trace_xfs_refcount_find_right_extent(cur->bc_mp, cur->bc_private.a.agno,
+                        cright, right, agbno + aglen);
+        return error;
+
+out_error:
+        trace_xfs_refcount_find_right_extent_error(cur->bc_mp,
+                        cur->bc_private.a.agno, error, _RET_IP_);
+        return error;
+}
+
+/* Is this extent valid? */
+static inline bool
+xfs_refc_valid(
+        struct xfs_refcount_irec        *rc)
+{
+        return rc->rc_startblock != NULLAGBLOCK;
+}
+
+/*
+ * Try to merge with any extents on the boundaries of the adjustment range.
+ */
+STATIC int
+xfs_refcount_merge_extents(
+        struct xfs_btree_cur    *cur,
+        xfs_agblock_t           *agbno,
+        xfs_extlen_t            *aglen,
+        enum xfs_refc_adjust_op adjust,
+        bool                    *shape_changed)
+{
+        struct xfs_refcount_irec        left = {0}, cleft = {0};
+        struct xfs_refcount_irec        cright = {0}, right = {0};
+        int                             error;
+        unsigned long long              ulen;
+        bool                            cequal;
+
+        *shape_changed = false;
+        /*
+         * Find the extent just below agbno [left], just above agbno [cleft],
+         * just below (agbno + aglen) [cright], and just above (agbno + aglen)
+         * [right].
+         */
+        error = xfs_refcount_find_left_extents(cur, &left, &cleft, *agbno,
+                        *aglen);
+        if (error)
+                return error;
+        error = xfs_refcount_find_right_extents(cur, &right, &cright, *agbno,
+                        *aglen);
+        if (error)
+                return error;
+
+        /* No left or right extent to merge; exit. */
+        if (!xfs_refc_valid(&left) && !xfs_refc_valid(&right))
+                return 0;
+
+        cequal = (cleft.rc_startblock == cright.rc_startblock) &&
+                 (cleft.rc_blockcount == cright.rc_blockcount);
+
+        /* Try to merge left, cleft, and right.  cleft must == cright. */
+        ulen = (unsigned long long)left.rc_blockcount + cleft.rc_blockcount +
+                        right.rc_blockcount;
+        if (xfs_refc_valid(&left) && xfs_refc_valid(&right) &&
+            xfs_refc_valid(&cleft) && xfs_refc_valid(&cright) && cequal &&
+            left.rc_refcount == cleft.rc_refcount + adjust &&
+            right.rc_refcount == cleft.rc_refcount + adjust &&
+            ulen < MAXREFCEXTLEN) {
+                *shape_changed = true;
+                return xfs_refcount_merge_center_extents(cur, &left, &cleft,
+                                &right, ulen, agbno, aglen);
+        }
+
+        /* Try to merge left and cleft. */
+        ulen = (unsigned long long)left.rc_blockcount + cleft.rc_blockcount;
+        if (xfs_refc_valid(&left) && xfs_refc_valid(&cleft) &&
+            left.rc_refcount == cleft.rc_refcount + adjust &&
+            ulen < MAXREFCEXTLEN) {
+                *shape_changed = true;
+                error = xfs_refcount_merge_left_extent(cur, &left, &cleft,
+                                agbno, aglen);
+                if (error)
+                        return error;
+
+                /*
+                 * If we just merged left + cleft and cleft == cright,
+                 * we no longer have a cright to merge with right.  We're done.
+                 */
+                if (cequal)
+                        return 0;
+        }
+
+        /* Try to merge cright and right. */
+        ulen = (unsigned long long)right.rc_blockcount + cright.rc_blockcount;
+        if (xfs_refc_valid(&right) && xfs_refc_valid(&cright) &&
+            right.rc_refcount == cright.rc_refcount + adjust &&
+            ulen < MAXREFCEXTLEN) {
+                *shape_changed = true;
+                return xfs_refcount_merge_right_extent(cur, &right, &cright,
+                                agbno, aglen);
+        }
+
+        return error;
+}
+
+/*
+ * While we're adjusting the refcounts records of an extent, we have
+ * to keep an eye on the number of extents we're dirtying -- run too
+ * many in a single transaction and we'll exceed the transaction's
+ * reservation and crash the fs.  Each record adds 12 bytes to the
+ * log (plus any key updates) so we'll conservatively assume 24 bytes
+ * per record.  We must also leave space for btree splits on both ends
+ * of the range and space for the CUD and a new CUI.
+ *
+ * XXX: This is a pretty hand-wavy estimate.  The penalty for guessing
+ * true incorrectly is a shutdown FS; the penalty for guessing false
+ * incorrectly is more transaction rolls than might be necessary.
+ * Be conservative here.
+ */
+static bool
+xfs_refcount_still_have_space(
+        struct xfs_btree_cur            *cur)
+{
+        unsigned long                   overhead;
+
+        overhead = cur->bc_private.a.priv.refc.shape_changes *
+                        xfs_allocfree_log_count(cur->bc_mp, 1);
+        overhead *= cur->bc_mp->m_sb.sb_blocksize;
+
+        /*
+         * Only allow 2 refcount extent updates per transaction if the
+         * refcount continue update "error" has been injected.
+         */
+        if (cur->bc_private.a.priv.refc.nr_ops > 2 &&
+            XFS_TEST_ERROR(false, cur->bc_mp,
+                        XFS_ERRTAG_REFCOUNT_CONTINUE_UPDATE,
+                        XFS_RANDOM_REFCOUNT_CONTINUE_UPDATE))
+                return false;
+
+        if (cur->bc_private.a.priv.refc.nr_ops == 0)
+                return true;
+        else if (overhead > cur->bc_tp->t_log_res)
+                return false;
+        return  cur->bc_tp->t_log_res - overhead >
+                cur->bc_private.a.priv.refc.nr_ops * 32;
+}
+
+/*
+ * Adjust the refcounts of middle extents.  At this point we should have
+ * split extents that crossed the adjustment range; merged with adjacent
+ * extents; and updated agbno/aglen to reflect the merges.  Therefore,
+ * all we have to do is update the extents inside [agbno, agbno + aglen].
+ */
+STATIC int
+xfs_refcount_adjust_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;
+        xfs_fsblock_t                   fsbno;
+
+        /* Merging did all the work already. */
+        if (*aglen == 0)
+                return 0;
+
+        error = xfs_refcount_lookup_ge(cur, *agbno, &found_rec);
+        if (error)
+                goto out_error;
+
+        while (*aglen > 0 && xfs_refcount_still_have_space(cur)) {
+                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;
+                        ext.rc_blockcount = 0;
+                        ext.rc_refcount = 0;
+                }
+
+                /*
+                 * Deal with a hole in the refcount tree; if a file maps to
+                 * these blocks and there's no refcountbt record, pretend that
+                 * there is one with refcount == 1.
+                 */
+                if (ext.rc_startblock != *agbno) {
+                        tmp.rc_startblock = *agbno;
+                        tmp.rc_blockcount = min(*aglen,
+                                        ext.rc_startblock - *agbno);
+                        tmp.rc_refcount = 1 + adj;
+                        trace_xfs_refcount_modify_extent(cur->bc_mp,
+                                        cur->bc_private.a.agno, &tmp);
+
+                        /*
+                         * Either cover the hole (increment) or
+                         * delete the range (decrement).
+                         */
+                        if (tmp.rc_refcount) {
+                                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);
+                                cur->bc_private.a.priv.refc.nr_ops++;
+                        } else {
+                                fsbno = XFS_AGB_TO_FSB(cur->bc_mp,
+                                                cur->bc_private.a.agno,
+                                                tmp.rc_startblock);
+                                xfs_bmap_add_free(cur->bc_mp, dfops, fsbno,
+                                                tmp.rc_blockcount, oinfo);
+                        }
+
+                        (*agbno) += tmp.rc_blockcount;
+                        (*aglen) -= tmp.rc_blockcount;
+
+                        error = xfs_refcount_lookup_ge(cur, *agbno,
+                                        &found_rec);
+                        if (error)
+                                goto out_error;
+                }
+
+                /* Stop if there's nothing left to modify */
+                if (*aglen == 0 || !xfs_refcount_still_have_space(cur))
+                        break;
+
+                /*
+                 * Adjust the reference count and either update the tree
+                 * (incr) or free the blocks (decr).
+                 */
+                if (ext.rc_refcount == MAXREFCOUNT)
+                        goto skip;
+                ext.rc_refcount += adj;
+                trace_xfs_refcount_modify_extent(cur->bc_mp,
+                                cur->bc_private.a.agno, &ext);
+                if (ext.rc_refcount > 1) {
+                        error = xfs_refcount_update(cur, &ext);
+                        if (error)
+                                goto out_error;
+                        cur->bc_private.a.priv.refc.nr_ops++;
+                } else if (ext.rc_refcount == 1) {
+                        error = xfs_refcount_delete(cur, &found_rec);
+                        if (error)
+                                goto out_error;
+                        XFS_WANT_CORRUPTED_GOTO(cur->bc_mp,
+                                        found_rec == 1, out_error);
+                        cur->bc_private.a.priv.refc.nr_ops++;
+                        goto advloop;
+                } else {
+                        fsbno = XFS_AGB_TO_FSB(cur->bc_mp,
+                                        cur->bc_private.a.agno,
+                                        ext.rc_startblock);
+                        xfs_bmap_add_free(cur->bc_mp, dfops, fsbno,
+                                        ext.rc_blockcount, oinfo);
+                }
+
+skip:
+                error = xfs_btree_increment(cur, 0, &found_rec);
+                if (error)
+                        goto out_error;
+
+advloop:
+                (*agbno) += ext.rc_blockcount;
+                (*aglen) -= ext.rc_blockcount;
+        }
+
+        return error;
+out_error:
+        trace_xfs_refcount_modify_extent_error(cur->bc_mp,
+                        cur->bc_private.a.agno, error, _RET_IP_);
+        return error;
+}
+
+/* Adjust the reference count of a range of AG blocks. */
+STATIC int
+xfs_refcount_adjust(
+        struct xfs_btree_cur    *cur,
+        xfs_agblock_t           agbno,
+        xfs_extlen_t            aglen,
+        xfs_agblock_t           *new_agbno,
+        xfs_extlen_t            *new_aglen,
+        enum xfs_refc_adjust_op adj,
+        struct xfs_defer_ops    *dfops,
+        struct xfs_owner_info   *oinfo)
+{
+        bool                    shape_changed;
+        int                     shape_changes = 0;
+        int                     error;
+
+        *new_agbno = agbno;
+        *new_aglen = aglen;
+        if (adj == XFS_REFCOUNT_ADJUST_INCREASE)
+                trace_xfs_refcount_increase(cur->bc_mp, cur->bc_private.a.agno,
+                                agbno, aglen);
+        else
+                trace_xfs_refcount_decrease(cur->bc_mp, cur->bc_private.a.agno,
+                                agbno, aglen);
+
+        /*
+         * 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;
+        if (shape_changed)
+                shape_changes++;
+
+        error = xfs_refcount_split_extent(cur, agbno + aglen, &shape_changed);
+        if (error)
+                goto out_error;
+        if (shape_changed)
+                shape_changes++;
+
+        /*
+         * 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);
+        if (error)
+                goto out_error;
+        if (shape_changed)
+                shape_changes++;
+        if (shape_changes)
+                cur->bc_private.a.priv.refc.shape_changes++;
+
+        /* Now that we've taken care of the ends, adjust the middle extents */
+        error = xfs_refcount_adjust_extents(cur, new_agbno, new_aglen,
+                        adj, dfops, oinfo);
+        if (error)
+                goto out_error;
+
+        return 0;
+
+out_error:
+        trace_xfs_refcount_adjust_error(cur->bc_mp, cur->bc_private.a.agno,
+                        error, _RET_IP_);
+        return error;
+}
diff --git a/fs/xfs/xfs_error.h b/fs/xfs/xfs_error.h
index 3d224702fbc0..d9675c646572 100644
--- a/fs/xfs/xfs_error.h
+++ b/fs/xfs/xfs_error.h
@@ -92,7 +92,8 @@ extern void xfs_verifier_error(struct xfs_buf *bp);
 #define XFS_ERRTAG_BMAPIFORMAT                          21
 #define XFS_ERRTAG_FREE_EXTENT                          22
 #define XFS_ERRTAG_RMAP_FINISH_ONE                      23
-#define XFS_ERRTAG_MAX                                  24
+#define XFS_ERRTAG_REFCOUNT_CONTINUE_UPDATE             24
+#define XFS_ERRTAG_MAX                                  25
 
 /*
  * Random factors for above tags, 1 means always, 2 means 1/2 time, etc.
@@ -121,6 +122,7 @@ extern void xfs_verifier_error(struct xfs_buf *bp);
 #define XFS_RANDOM_BMAPIFORMAT                          XFS_RANDOM_DEFAULT
 #define XFS_RANDOM_FREE_EXTENT                          1
 #define XFS_RANDOM_RMAP_FINISH_ONE                      1
+#define XFS_RANDOM_REFCOUNT_CONTINUE_UPDATE             1
 
 #ifdef DEBUG
 extern int xfs_error_test_active;