[PATCH 1/1] xfs: make xchk_iget safer in the presence of corrupt inode btrees

["Darrick J. Wong" <djwong@xxxxxxxxxx>]

From: Darrick J. Wong <djwong@xxxxxxxxxx>

When scrub is trying to iget na 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@xxxxxxxxxx>
---
 fs/xfs/scrub/common.c |    6 ++++--
 fs/xfs/scrub/common.h |   19 +++++++++++++++++++
 fs/xfs/scrub/inode.c  |    4 ++--
 3 files changed, 25 insertions(+), 4 deletions(-)


diff --git a/fs/xfs/scrub/common.c b/fs/xfs/scrub/common.c
index de24532fe0830..23944fcc1a6ca 100644
--- a/fs/xfs/scrub/common.c
+++ b/fs/xfs/scrub/common.c
@@ -733,6 +733,8 @@ xchk_iget(
 	xfs_ino_t		inum,
 	struct xfs_inode	**ipp)
 {
+	ASSERT(sc->tp != NULL);
+
 	return xfs_iget(sc->mp, sc->tp, inum, XFS_IGET_UNTRUSTED, 0, ipp);
 }
 
@@ -882,8 +884,8 @@ xchk_iget_for_scrubbing(
 	if (!xfs_verify_ino(sc->mp, sc->sm->sm_ino))
 		return -ENOENT;
 
-	/* Try a regular untrusted iget. */
-	error = xchk_iget(sc, sc->sm->sm_ino, &ip);
+	/* Try a safe untrusted iget. */
+	error = xchk_iget_safe(sc, sc->sm->sm_ino, &ip);
 	if (!error)
 		return xchk_install_handle_inode(sc, ip);
 	if (error == -ENOENT)
diff --git a/fs/xfs/scrub/common.h b/fs/xfs/scrub/common.h
index cabdc0e16838c..a39dbe6be1e59 100644
--- a/fs/xfs/scrub/common.h
+++ b/fs/xfs/scrub/common.h
@@ -157,6 +157,25 @@ int xchk_iget_agi(struct xfs_scrub *sc, xfs_ino_t inum,
 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.
+ */
+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.
diff --git a/fs/xfs/scrub/inode.c b/fs/xfs/scrub/inode.c
index 59d7912fb75f1..74b1ebb40a4c0 100644
--- a/fs/xfs/scrub/inode.c
+++ b/fs/xfs/scrub/inode.c
@@ -94,8 +94,8 @@ xchk_setup_inode(
 	if (!xfs_verify_ino(sc->mp, sc->sm->sm_ino))
 		return -ENOENT;
 
-	/* Try a regular untrusted iget. */
-	error = xchk_iget(sc, sc->sm->sm_ino, &ip);
+	/* Try a safe untrusted iget. */
+	error = xchk_iget_safe(sc, sc->sm->sm_ino, &ip);
 	if (!error)
 		return xchk_install_handle_iscrub(sc, ip);
 	if (error == -ENOENT)