[PATCH 4/4] xfs: ask the dentry cache if it knows the parent of a directory

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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.

Signed-off-by: Darrick J. Wong <djwong@xxxxxxxxxx>
---
 fs/xfs/scrub/dir_repair.c    |   29 +++++++++++++++++++++++++++++
 fs/xfs/scrub/findparent.c    |   41 ++++++++++++++++++++++++++++++++++++++++-
 fs/xfs/scrub/findparent.h    |    1 +
 fs/xfs/scrub/parent_repair.c |   13 +++++++++++++
 fs/xfs/scrub/trace.h         |    1 +
 5 files changed, 84 insertions(+), 1 deletion(-)


diff --git a/fs/xfs/scrub/dir_repair.c b/fs/xfs/scrub/dir_repair.c
index 297935416aed6..b22fd59c2f8b3 100644
--- a/fs/xfs/scrub/dir_repair.c
+++ b/fs/xfs/scrub/dir_repair.c
@@ -206,6 +206,29 @@ 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(
@@ -219,6 +242,12 @@ 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 b8716e881e62e..87047e9d49e47 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 +411,41 @@ 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;
+
+	if (parent->d_sb != sc->ip->i_mount->m_super) {
+		dput(parent);
+		goto out_dput;
+	}
+
+	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 5876bf661578e..cb3a97f3fed48 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 8b8bc7b1f5a5b..430f95171b50b 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 7590fca158417..5ccb92214a80d 100644
--- a/fs/xfs/scrub/trace.h
+++ b/fs/xfs/scrub/trace.h
@@ -2694,6 +2694,7 @@ 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) */
 





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