xfs: make xchk_iget safer in the presence of corrupt inode btrees

When scrub is trying to iget an inode, ensure that it won't end up
deadlocked on a cycle in the inode btree by using an empty transaction
to store all the buffers.

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

1 files changed, 25 insertions, 0 deletions

diff --git a/fs/xfs/scrub/common.h b/fs/xfs/scrub/common.h
index cabdc0e16838..c83cf9e5b55f 100644
--- a/fs/xfs/scrub/common.h
+++ b/fs/xfs/scrub/common.h
@@ -151,6 +151,11 @@ void xchk_iunlock(struct xfs_scrub *sc, unsigned int ilock_flags);
 
 void xchk_buffer_recheck(struct xfs_scrub *sc, struct xfs_buf *bp);
 
+/*
+ * Grab the inode at @inum.  The caller must have created a scrub transaction
+ * so that we can confirm the inumber by walking the inobt and not deadlock on
+ * a loop in the inobt.
+ */
 int xchk_iget(struct xfs_scrub *sc, xfs_ino_t inum, struct xfs_inode **ipp);
 int xchk_iget_agi(struct xfs_scrub *sc, xfs_ino_t inum,
 		struct xfs_buf **agi_bpp, struct xfs_inode **ipp);
@@ -158,6 +163,26 @@ void xchk_irele(struct xfs_scrub *sc, struct xfs_inode *ip);
 int xchk_install_handle_inode(struct xfs_scrub *sc, struct xfs_inode *ip);
 
 /*
+ * Safe version of (untrusted) xchk_iget that uses an empty transaction to
+ * avoid deadlocking on loops in the inobt.  This should only be used in a
+ * scrub or repair setup routine, and only prior to grabbing a transaction.
+ */
+static inline int
+xchk_iget_safe(struct xfs_scrub *sc, xfs_ino_t inum, struct xfs_inode **ipp)
+{
+	int	error;
+
+	ASSERT(sc->tp == NULL);
+
+	error = xchk_trans_alloc(sc, 0);
+	if (error)
+		return error;
+	error = xchk_iget(sc, inum, ipp);
+	xchk_trans_cancel(sc);
+	return error;
+}
+
+/*
  * Don't bother cross-referencing if we already found corruption or cross
  * referencing discrepancies.
  */