xfs: abort directory parent scrub scans if we encounter a zapped directory

In a previous patch, we added some code to perform sufficient repairs
to an ondisk inode record such that the inode cache would be willing to
load the inode.  If the broken inode was a shortform directory, it will
reset the directory to something plausible, which is to say an empty
subdirectory of the root.  The telltale signs that something is
seriously wrong is the broken link count.

Such directories look clean, but they shouldn't participate in a
filesystem scan to find or confirm a directory parent pointer.  Create a
predicate that identifies such directories and abort the scrub.

Found by fuzzing xfs/1554 with multithreaded xfs_scrub enabled and
u3.bmx[0].startblock = zeroes.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>

1 files changed, 26 insertions, 0 deletions

diff --git a/fs/xfs/scrub/dir.c b/fs/xfs/scrub/dir.c
index b366fab699ac..d86ab51af928 100644
--- a/fs/xfs/scrub/dir.c
+++ b/fs/xfs/scrub/dir.c
@@ -798,3 +798,29 @@ xchk_directory(
 	xchk_mark_healthy_if_clean(sc, XFS_SICK_INO_DIR_ZAPPED);
 	return 0;
 }
+
+/*
+ * Decide if this directory has been zapped to satisfy the inode and ifork
+ * verifiers.  Checking and repairing should be postponed until the directory
+ * is fixed.
+ */
+bool
+xchk_dir_looks_zapped(
+	struct xfs_inode	*dp)
+{
+	/* Repair zapped this dir's data fork a short time ago */
+	if (xfs_ifork_zapped(dp, XFS_DATA_FORK))
+		return true;
+
+	/*
+	 * If the dinode repair found a bad data fork, it will reset the fork
+	 * to extents format with zero records and wait for the bmapbtd
+	 * scrubber to reconstruct the block mappings.  Directories always
+	 * contain some content, so this is a clear sign of a zapped directory.
+	 * The state checked by xfs_ifork_zapped is not persisted, so this is
+	 * the secondary strategy if repairs are interrupted by a crash or an
+	 * unmount.
+	 */
+	return dp->i_df.if_format == XFS_DINODE_FMT_EXTENTS &&
+	       dp->i_df.if_nextents == 0;
+}