xfs: don't be so eager to clear the cowblocks tag on truncate

Currently, xfs_itruncate_extents clears the cowblocks tag if i_cnextents
is zero.  This is wrong, since i_cnextents only tracks real extents in
the CoW fork, which means that we could have some delayed CoW
reservations still in there that will now never get cleaned.

Fix a further bug where we /don't/ clear the reflink iflag if there are
any attribute blocks -- really, it's only safe to clear the reflink flag
if there are no data fork extents and no cow fork extents.

Found by adding clonerange to fsstress in xfs/017.

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

1 files changed, 19 insertions, 9 deletions

diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
index b41952a4ddd8..6f95bdb408ce 100644
--- a/fs/xfs/xfs_inode.c
+++ b/fs/xfs/xfs_inode.c
@@ -1487,6 +1487,24 @@ xfs_link(
         return error;
 }
 
+/* Clear the reflink flag and the cowblocks tag if possible. */
+static void
+xfs_itruncate_clear_reflink_flags(
+        struct xfs_inode        *ip)
+{
+        struct xfs_ifork        *dfork;
+        struct xfs_ifork        *cfork;
+
+        if (!xfs_is_reflink_inode(ip))
+                return;
+        dfork = XFS_IFORK_PTR(ip, XFS_DATA_FORK);
+        cfork = XFS_IFORK_PTR(ip, XFS_COW_FORK);
+        if (dfork->if_bytes == 0 && cfork->if_bytes == 0)
+                ip->i_d.di_flags2 &= ~XFS_DIFLAG2_REFLINK;
+        if (cfork->if_bytes == 0)
+                xfs_inode_clear_cowblocks_tag(ip);
+}
+
 /*
  * Free up the underlying blocks past new_size.  The new size must be smaller
  * than the current size.  This routine can be used both for the attribute and
@@ -1583,15 +1601,7 @@ xfs_itruncate_extents(
         if (error)
                 goto out;
 
-        /*
-         * Clear the reflink flag if there are no data fork blocks and
-         * there are no extents staged in the cow fork.
-         */
-        if (xfs_is_reflink_inode(ip) && ip->i_cnextents == 0) {
-                if (ip->i_d.di_nblocks == 0)
-                        ip->i_d.di_flags2 &= ~XFS_DIFLAG2_REFLINK;
-                xfs_inode_clear_cowblocks_tag(ip);
-        }
+        xfs_itruncate_clear_reflink_flags(ip);
 
         /*
          * Always re-log the inode so that our permanent transaction can keep