From: Darrick J. Wong <djwong@xxxxxxxxxx>
It's possible that the dentry cache can tell us the parent of a
directory. Therefore, when repairing directory dot dot entries, query
the dcache as a last resort before scanning the entire filesystem.
A reviewer asks:
"How high is the chance that we actually have a valid dcache entry for a
file in a corrupted directory?"
There's a decent chance of this actually working. Say you have a
1000-block directory foo, and block 980 gets corrupted. Let's further
suppose that block 0 has a correct entry for ".." and "bar". If someone
accesses /mnt/foo/bar, that will cause the dcache to create a dentry
from /mnt to /mnt/foo whose d_parent points back to /mnt. If you then
want to rebuild the directory, XFS can obtain the parent from the dcache
without needing to wander into parent pointers or scan the filesystem to
find /mnt's connection to foo.
Signed-off-by: Darrick J. Wong <djwong@xxxxxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
---
fs/xfs/scrub/dir_repair.c | 29 +++++++++++++++++++++++++++++
fs/xfs/scrub/findparent.c | 38 +++++++++++++++++++++++++++++++++++++-
fs/xfs/scrub/findparent.h | 1 +
fs/xfs/scrub/parent_repair.c | 13 +++++++++++++
fs/xfs/scrub/trace.h | 1 +
5 files changed, 81 insertions(+), 1 deletion(-)
diff --git a/fs/xfs/scrub/dir_repair.c b/fs/xfs/scrub/dir_repair.c
index b17de79207db..34fe720fde0e 100644
--- a/fs/xfs/scrub/dir_repair.c
+++ b/fs/xfs/scrub/dir_repair.c
@@ -208,6 +208,29 @@ xrep_dir_lookup_parent(
return ino;
}
+/*
+ * Look up '..' in the dentry cache and confirm that it's really the parent.
+ * Returns NULLFSINO if the dcache misses or if the hit is implausible.
+ */
+static inline xfs_ino_t
+xrep_dir_dcache_parent(
+ struct xrep_dir *rd)
+{
+ struct xfs_scrub *sc = rd->sc;
+ xfs_ino_t parent_ino;
+ int error;
+
+ parent_ino = xrep_findparent_from_dcache(sc);
+ if (parent_ino == NULLFSINO)
+ return parent_ino;
+
+ error = xrep_findparent_confirm(sc, &parent_ino);
+ if (error)
+ return NULLFSINO;
+
+ return parent_ino;
+}
+
/* Try to find the parent of the directory being repaired. */
STATIC int
xrep_dir_find_parent(
@@ -221,6 +244,12 @@ xrep_dir_find_parent(
return 0;
}
+ ino = xrep_dir_dcache_parent(rd);
+ if (ino != NULLFSINO) {
+ xrep_findparent_scan_finish_early(&rd->pscan, ino);
+ return 0;
+ }
+
ino = xrep_dir_lookup_parent(rd);
if (ino != NULLFSINO) {
xrep_findparent_scan_finish_early(&rd->pscan, ino);
diff --git a/fs/xfs/scrub/findparent.c b/fs/xfs/scrub/findparent.c
index 7b3ec8d7d6cc..712dd73e4789 100644
--- a/fs/xfs/scrub/findparent.c
+++ b/fs/xfs/scrub/findparent.c
@@ -53,7 +53,8 @@
* must not read the scan results without re-taking @sc->ip's ILOCK.
*
* There are a few shortcuts that we can take to avoid scanning the entire
- * filesystem, such as noticing directory tree roots.
+ * filesystem, such as noticing directory tree roots and querying the dentry
+ * cache for parent information.
*/
struct xrep_findparent_info {
@@ -410,3 +411,38 @@ xrep_findparent_self_reference(
return NULLFSINO;
}
+
+/* Check the dentry cache to see if knows of a parent for the scrub target. */
+xfs_ino_t
+xrep_findparent_from_dcache(
+ struct xfs_scrub *sc)
+{
+ struct inode *pip = NULL;
+ struct dentry *dentry, *parent;
+ xfs_ino_t ret = NULLFSINO;
+
+ dentry = d_find_alias(VFS_I(sc->ip));
+ if (!dentry)
+ goto out;
+
+ parent = dget_parent(dentry);
+ if (!parent)
+ goto out_dput;
+
+ ASSERT(parent->d_sb == sc->ip->i_mount->m_super);
+
+ pip = igrab(d_inode(parent));
+ dput(parent);
+
+ if (S_ISDIR(pip->i_mode)) {
+ trace_xrep_findparent_from_dcache(sc->ip, XFS_I(pip)->i_ino);
+ ret = XFS_I(pip)->i_ino;
+ }
+
+ xchk_irele(sc, XFS_I(pip));
+
+out_dput:
+ dput(dentry);
+out:
+ return ret;
+}
diff --git a/fs/xfs/scrub/findparent.h b/fs/xfs/scrub/findparent.h
index d946bc81f34e..501f99d3164e 100644
--- a/fs/xfs/scrub/findparent.h
+++ b/fs/xfs/scrub/findparent.h
@@ -45,5 +45,6 @@ void xrep_findparent_scan_finish_early(struct xrep_parent_scan_info *pscan,
int xrep_findparent_confirm(struct xfs_scrub *sc, xfs_ino_t *parent_ino);
xfs_ino_t xrep_findparent_self_reference(struct xfs_scrub *sc);
+xfs_ino_t xrep_findparent_from_dcache(struct xfs_scrub *sc);
#endif /* __XFS_SCRUB_FINDPARENT_H__ */
diff --git a/fs/xfs/scrub/parent_repair.c b/fs/xfs/scrub/parent_repair.c
index 0a9651bb0b05..826926c2bb0d 100644
--- a/fs/xfs/scrub/parent_repair.c
+++ b/fs/xfs/scrub/parent_repair.c
@@ -118,7 +118,20 @@ xrep_parent_find_dotdot(
* then retake the ILOCK so that we can salvage directory entries.
*/
xchk_iunlock(sc, XFS_ILOCK_EXCL);
+
+ /* Does the VFS dcache have an answer for us? */
+ ino = xrep_findparent_from_dcache(sc);
+ if (ino != NULLFSINO) {
+ error = xrep_findparent_confirm(sc, &ino);
+ if (!error && ino != NULLFSINO) {
+ xrep_findparent_scan_finish_early(&rp->pscan, ino);
+ goto out_relock;
+ }
+ }
+
+ /* Scan the entire filesystem for a parent. */
error = xrep_findparent_scan(&rp->pscan);
+out_relock:
xchk_ilock(sc, XFS_ILOCK_EXCL);
return error;
diff --git a/fs/xfs/scrub/trace.h b/fs/xfs/scrub/trace.h
index e1755fe63e67..d68ec8e2781e 100644
--- a/fs/xfs/scrub/trace.h
+++ b/fs/xfs/scrub/trace.h
@@ -2613,6 +2613,7 @@ DEFINE_EVENT(xrep_parent_salvage_class, name, \
TP_ARGS(dp, ino))
DEFINE_XREP_PARENT_SALVAGE_EVENT(xrep_dir_salvaged_parent);
DEFINE_XREP_PARENT_SALVAGE_EVENT(xrep_findparent_dirent);
+DEFINE_XREP_PARENT_SALVAGE_EVENT(xrep_findparent_from_dcache);
#endif /* IS_ENABLED(CONFIG_XFS_ONLINE_REPAIR) */
