Merge: xfs: estimate post-merge refcounts correctly

MR: https://gitlab.com/redhat/centos-stream/src/kernel/centos-stream-9/-/merge_requests/1927

xfs: estimate post-merge refcounts correctly

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2161676

xfs/179 fails after it was recently modified for reproducing a bug regarding refcount overflowing:
https://git.kernel.org/pub/scm/fs/xfs/xfstests-dev.git/commit/?h=for-next&id=56c8f841407c29808d370d06929a3f58c7afeee3

fixed by:
9d720a5: xfs: hoist refcount record merge predicates
b25d198: xfs: estimate post-merge refcounts correctly

  commit b25d198
  Author: Darrick J. Wong <djwong@kernel.org>
  Date:   Wed Nov 30 09:25:51 2022 -0800

    xfs: estimate post-merge refcounts correctly

    Upon enabling fsdax + reflink for XFS, xfs/179 began to report refcount
    metadata corruptions after being run.  Specifically, xfs_repair noticed
    single-block refcount records that could be combined but had not been.

    The root cause of this is improper MAXREFCOUNT edge case handling in
    xfs_refcount_merge_extents.  When we're trying to find candidates for a
    refcount btree record merge, we compute the refcount attribute of the
    merged record, but we fail to account for the fact that once a record
    hits rc_refcount == MAXREFCOUNT, it is pinned that way forever.  Hence
    the computed refcount is wrong, and we fail to merge the extents.
    Fix this by adjusting the merge predicates to compute the adjusted
    refcount correctly.

    Fixes: 3172725 ("xfs: adjust refcount of an extent of blocks in refcount btree")
    Signed-off-by: Darrick J. Wong <djwong@kernel.org>
    Reviewed-by: Dave Chinner <dchinner@redhat.com>
    Reviewed-by: Xiao Yang <yangx.jy@fujitsu.com>

Signed-off-by: Bill O'Donnell <bodonnel@redhat.com>

Approved-by: Brian Foster <bfoster@redhat.com>
Approved-by: Eric Sandeen <esandeen@redhat.com>

Signed-off-by: Herton R. Krzesinski <herton@redhat.com>

Author: Herton R. Krzesinski

fs/xfs/libxfs/xfs_refcount.c

@@ -784,11 +784,136 @@ xfs_refcount_find_right_extents(
 /* Is this extent valid? */
 static inline bool
 xfs_refc_valid(
-	struct xfs_refcount_irec	*rc)
+	const struct xfs_refcount_irec	*rc)
 {
 	return rc->rc_startblock != NULLAGBLOCK;
 }
 
+static inline xfs_nlink_t
+xfs_refc_merge_refcount(
+	const struct xfs_refcount_irec	*irec,
+	enum xfs_refc_adjust_op		adjust)
+{
+	/* Once a record hits MAXREFCOUNT, it is pinned there forever */
+	if (irec->rc_refcount == MAXREFCOUNT)
+		return MAXREFCOUNT;
+	return irec->rc_refcount + adjust;
+}
+
+static inline bool
+xfs_refc_want_merge_center(
+	const struct xfs_refcount_irec	*left,
+	const struct xfs_refcount_irec	*cleft,
+	const struct xfs_refcount_irec	*cright,
+	const struct xfs_refcount_irec	*right,
+	bool				cleft_is_cright,
+	enum xfs_refc_adjust_op		adjust,
+	unsigned long long		*ulenp)
+{
+	unsigned long long		ulen = left->rc_blockcount;
+	xfs_nlink_t			new_refcount;
+
+	/*
+	 * To merge with a center record, both shoulder records must be
+	 * adjacent to the record we want to adjust.  This is only true if
+	 * find_left and find_right made all four records valid.
+	 */
+	if (!xfs_refc_valid(left)  || !xfs_refc_valid(right) ||
+	    !xfs_refc_valid(cleft) || !xfs_refc_valid(cright))
+		return false;
+
+	/* There must only be one record for the entire range. */
+	if (!cleft_is_cright)
+		return false;
+
+	/* The shoulder record refcounts must match the new refcount. */
+	new_refcount = xfs_refc_merge_refcount(cleft, adjust);
+	if (left->rc_refcount != new_refcount)
+		return false;
+	if (right->rc_refcount != new_refcount)
+		return false;
+
+	/*
+	 * The new record cannot exceed the max length.  ulen is a ULL as the
+	 * individual record block counts can be up to (u32 - 1) in length
+	 * hence we need to catch u32 addition overflows here.
+	 */
+	ulen += cleft->rc_blockcount + right->rc_blockcount;
+	if (ulen >= MAXREFCEXTLEN)
+		return false;
+
+	*ulenp = ulen;
+	return true;
+}
+
+static inline bool
+xfs_refc_want_merge_left(
+	const struct xfs_refcount_irec	*left,
+	const struct xfs_refcount_irec	*cleft,
+	enum xfs_refc_adjust_op		adjust)
+{
+	unsigned long long		ulen = left->rc_blockcount;
+	xfs_nlink_t			new_refcount;
+
+	/*
+	 * For a left merge, the left shoulder record must be adjacent to the
+	 * start of the range.  If this is true, find_left made left and cleft
+	 * contain valid contents.
+	 */
+	if (!xfs_refc_valid(left) || !xfs_refc_valid(cleft))
+		return false;
+
+	/* Left shoulder record refcount must match the new refcount. */
+	new_refcount = xfs_refc_merge_refcount(cleft, adjust);
+	if (left->rc_refcount != new_refcount)
+		return false;
+
+	/*
+	 * The new record cannot exceed the max length.  ulen is a ULL as the
+	 * individual record block counts can be up to (u32 - 1) in length
+	 * hence we need to catch u32 addition overflows here.
+	 */
+	ulen += cleft->rc_blockcount;
+	if (ulen >= MAXREFCEXTLEN)
+		return false;
+
+	return true;
+}
+
+static inline bool
+xfs_refc_want_merge_right(
+	const struct xfs_refcount_irec	*cright,
+	const struct xfs_refcount_irec	*right,
+	enum xfs_refc_adjust_op		adjust)
+{
+	unsigned long long		ulen = right->rc_blockcount;
+	xfs_nlink_t			new_refcount;
+
+	/*
+	 * For a right merge, the right shoulder record must be adjacent to the
+	 * end of the range.  If this is true, find_right made cright and right
+	 * contain valid contents.
+	 */
+	if (!xfs_refc_valid(right) || !xfs_refc_valid(cright))
+		return false;
+
+	/* Right shoulder record refcount must match the new refcount. */
+	new_refcount = xfs_refc_merge_refcount(cright, adjust);
+	if (right->rc_refcount != new_refcount)
+		return false;
+
+	/*
+	 * The new record cannot exceed the max length.  ulen is a ULL as the
+	 * individual record block counts can be up to (u32 - 1) in length
+	 * hence we need to catch u32 addition overflows here.
+	 */
+	ulen += cright->rc_blockcount;
+	if (ulen >= MAXREFCEXTLEN)
+		return false;
+
+	return true;
+}
+
 /*
  * Try to merge with any extents on the boundaries of the adjustment range.
  */
@@ -830,23 +955,15 @@ xfs_refcount_merge_extents(
 		 (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) {
+	if (xfs_refc_want_merge_center(&left, &cleft, &cright, &right, cequal,
+				adjust, &ulen)) {
 		*shape_changed = true;
 		return xfs_refcount_merge_center_extents(cur, &left, &cleft,
 				&right, ulen, 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) {
+	if (xfs_refc_want_merge_left(&left, &cleft, adjust)) {
 		*shape_changed = true;
 		error = xfs_refcount_merge_left_extent(cur, &left, &cleft,
 				agbno, aglen);
@@ -862,10 +979,7 @@ xfs_refcount_merge_extents(
 	}
 
 	/* 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) {
+	if (xfs_refc_want_merge_right(&cright, &right, adjust)) {
 		*shape_changed = true;
 		return xfs_refcount_merge_right_extent(cur, &right, &cright,
 				aglen);