Merge tag 'scrub-pptrs-6.10_2024-04-23' of...

Merge tag 'scrub-pptrs-6.10_2024-04-23' of https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux into xfs-6.10-mergeC

xfs: scrubbing for parent pointers

Teach online fsck to use parent pointers to assist in checking
directories, parent pointers, extended attributes, and link counts.
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>

* tag 'scrub-pptrs-6.10_2024-04-23' of https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux:
  xfs: check parent pointer xattrs when scrubbing
  xfs: walk directory parent pointers to determine backref count
  xfs: deferred scrub of parent pointers
  xfs: scrub parent pointers
  xfs: deferred scrub of dirents
  xfs: check dirents have parent pointers
  xfs: revert commit 44af6c7e

fs/xfs/Makefile

@@ -177,6 +177,7 @@ xfs-y				+= $(addprefix scrub/, \
 				   scrub.o \
 				   symlink.o \
 				   xfarray.o \
+				   xfblob.o \
 				   xfile.o \
 				   )
 
@@ -218,7 +219,6 @@ xfs-y				+= $(addprefix scrub/, \
 				   rmap_repair.o \
 				   symlink_repair.o \
 				   tempfile.o \
-				   xfblob.o \
 				   )
 
 xfs-$(CONFIG_XFS_RT)		+= $(addprefix scrub/, \

fs/xfs/libxfs/xfs_parent.c

@@ -291,3 +291,25 @@ xfs_parent_from_attr(
 		*parent_gen = be32_to_cpu(rec->p_gen);
 	return 0;
 }
+
+/*
+ * Look up a parent pointer record (@parent_name -> @pptr) of @ip.
+ *
+ * Caller must hold at least ILOCK_SHARED.  The scratchpad need not be
+ * initialized.
+ *
+ * Returns 0 if the pointer is found, -ENOATTR if there is no match, or a
+ * negative errno.
+ */
+int
+xfs_parent_lookup(
+	struct xfs_trans		*tp,
+	struct xfs_inode		*ip,
+	const struct xfs_name		*parent_name,
+	struct xfs_parent_rec		*pptr,
+	struct xfs_da_args		*scratch)
+{
+	memset(scratch, 0, sizeof(struct xfs_da_args));
+	xfs_parent_da_args_init(scratch, tp, pptr, ip, ip->i_ino, parent_name);
+	return xfs_attr_get_ilocked(scratch);
+}

fs/xfs/libxfs/xfs_parent.h

@@ -96,4 +96,9 @@ int xfs_parent_from_attr(struct xfs_mount *mp, unsigned int attr_flags,
 		const void *value, unsigned int valuelen,
 		xfs_ino_t *parent_ino, uint32_t *parent_gen);
 
+/* Repair functions */
+int xfs_parent_lookup(struct xfs_trans *tp, struct xfs_inode *ip,
+		const struct xfs_name *name, struct xfs_parent_rec *pptr,
+		struct xfs_da_args *scratch);
+
 #endif /* __XFS_PARENT_H__ */

fs/xfs/scrub/attr.c

@@ -17,6 +17,7 @@
 #include "xfs_attr.h"
 #include "xfs_attr_leaf.h"
 #include "xfs_attr_sf.h"
+#include "xfs_parent.h"
 #include "scrub/scrub.h"
 #include "scrub/common.h"
 #include "scrub/dabtree.h"
@@ -208,13 +209,12 @@ xchk_xattr_actor(
 		return -ECANCELED;
 	}
 
-	/*
-	 * Local and shortform xattr values are stored in the attr leaf block,
-	 * so we don't need to retrieve the value from a remote block to detect
-	 * corruption problems.
-	 */
-	if (value)
-		return 0;
+	/* Check parent pointer record. */
+	if ((attr_flags & XFS_ATTR_PARENT) &&
+	    !xfs_parent_valuecheck(sc->mp, value, valuelen)) {
+		xchk_fblock_set_corrupt(sc, XFS_ATTR_FORK, args.blkno);
+		return -ECANCELED;
+	}
 
 	/*
 	 * Try to allocate enough memory to extract the attr value.  If that
@@ -227,8 +227,21 @@ xchk_xattr_actor(
 	if (error)
 		return error;
 
+	/*
+	 * Parent pointers are matched on attr name and value, so we must
+	 * supply the xfs_parent_rec here when confirming that the dabtree
+	 * indexing works correctly.
+	 */
+	if (attr_flags & XFS_ATTR_PARENT)
+		memcpy(ab->value, value, valuelen);
+
 	args.value = ab->value;
 
+	/*
+	 * Get the attr value to ensure that lookup can find this attribute
+	 * through the dabtree indexing and that remote value retrieval also
+	 * works correctly.
+	 */
 	xfs_attr_sethash(&args);
 	error = xfs_attr_get_ilocked(&args);
 	/* ENODATA means the hash lookup failed and the attr is bad */

fs/xfs/scrub/common.h

@@ -212,6 +212,7 @@ static inline bool xchk_skip_xref(struct xfs_scrub_metadata *sm)
 }
 
 bool xchk_dir_looks_zapped(struct xfs_inode *dp);
+bool xchk_pptr_looks_zapped(struct xfs_inode *ip);
 
 #ifdef CONFIG_XFS_ONLINE_REPAIR
 /* Decide if a repair is required. */

fs/xfs/scrub/dir.c

@@ -16,12 +16,18 @@
 #include "xfs_dir2.h"
 #include "xfs_dir2_priv.h"
 #include "xfs_health.h"
+#include "xfs_attr.h"
+#include "xfs_parent.h"
 #include "scrub/scrub.h"
 #include "scrub/common.h"
 #include "scrub/dabtree.h"
 #include "scrub/readdir.h"
 #include "scrub/health.h"
 #include "scrub/repair.h"
+#include "scrub/trace.h"
+#include "scrub/xfile.h"
+#include "scrub/xfarray.h"
+#include "scrub/xfblob.h"
 
 /* Set us up to scrub directories. */
 int
@@ -41,6 +47,39 @@ xchk_setup_directory(
 
 /* Directories */
 
+/* Deferred directory entry that we saved for later. */
+struct xchk_dirent {
+	/* Cookie for retrieval of the dirent name. */
+	xfblob_cookie		name_cookie;
+
+	/* Child inode number. */
+	xfs_ino_t		ino;
+
+	/* Length of the pptr name. */
+	uint8_t			namelen;
+};
+
+struct xchk_dir {
+	struct xfs_scrub	*sc;
+
+	/* information for parent pointer validation. */
+	struct xfs_parent_rec	pptr_rec;
+	struct xfs_da_args	pptr_args;
+
+	/* Fixed-size array of xchk_dirent structures. */
+	struct xfarray		*dir_entries;
+
+	/* Blobs containing dirent names. */
+	struct xfblob		*dir_names;
+
+	/* If we've cycled the ILOCK, we must revalidate deferred dirents. */
+	bool			need_revalidate;
+
+	/* Name buffer for dirent revalidation. */
+	struct xfs_name		xname;
+	uint8_t			namebuf[MAXNAMELEN];
+};
+
 /* Scrub a directory entry. */
 
 /* Check that an inode's mode matches a given XFS_DIR3_FT_* type. */
@@ -63,6 +102,108 @@ xchk_dir_check_ftype(
 		xchk_fblock_set_corrupt(sc, XFS_DATA_FORK, offset);
 }
 
+/*
+ * Try to lock a child file for checking parent pointers.  Returns the inode
+ * flags for the locks we now hold, or zero if we failed.
+ */
+STATIC unsigned int
+xchk_dir_lock_child(
+	struct xfs_scrub	*sc,
+	struct xfs_inode	*ip)
+{
+	if (!xfs_ilock_nowait(ip, XFS_IOLOCK_SHARED))
+		return 0;
+
+	if (!xfs_ilock_nowait(ip, XFS_ILOCK_SHARED)) {
+		xfs_iunlock(ip, XFS_IOLOCK_SHARED);
+		return 0;
+	}
+
+	if (!xfs_inode_has_attr_fork(ip) || !xfs_need_iread_extents(&ip->i_af))
+		return XFS_IOLOCK_SHARED | XFS_ILOCK_SHARED;
+
+	xfs_iunlock(ip, XFS_ILOCK_SHARED);
+
+	if (!xfs_ilock_nowait(ip, XFS_ILOCK_EXCL)) {
+		xfs_iunlock(ip, XFS_IOLOCK_SHARED);
+		return 0;
+	}
+
+	return XFS_IOLOCK_SHARED | XFS_ILOCK_EXCL;
+}
+
+/* Check the backwards link (parent pointer) associated with this dirent. */
+STATIC int
+xchk_dir_parent_pointer(
+	struct xchk_dir		*sd,
+	const struct xfs_name	*name,
+	struct xfs_inode	*ip)
+{
+	struct xfs_scrub	*sc = sd->sc;
+	int			error;
+
+	xfs_inode_to_parent_rec(&sd->pptr_rec, sc->ip);
+	error = xfs_parent_lookup(sc->tp, ip, name, &sd->pptr_rec,
+			&sd->pptr_args);
+	if (error == -ENOATTR)
+		xchk_fblock_xref_set_corrupt(sc, XFS_DATA_FORK, 0);
+
+	return 0;
+}
+
+/* Look for a parent pointer matching this dirent, if the child isn't busy. */
+STATIC int
+xchk_dir_check_pptr_fast(
+	struct xchk_dir		*sd,
+	xfs_dir2_dataptr_t	dapos,
+	const struct xfs_name	*name,
+	struct xfs_inode	*ip)
+{
+	struct xfs_scrub	*sc = sd->sc;
+	unsigned int		lockmode;
+	int			error;
+
+	/* dot and dotdot entries do not have parent pointers */
+	if (xfs_dir2_samename(name, &xfs_name_dot) ||
+	    xfs_dir2_samename(name, &xfs_name_dotdot))
+		return 0;
+
+	/* No self-referential non-dot or dotdot dirents. */
+	if (ip == sc->ip) {
+		xchk_fblock_set_corrupt(sc, XFS_DATA_FORK, 0);
+		return -ECANCELED;
+	}
+
+	/* Try to lock the inode. */
+	lockmode = xchk_dir_lock_child(sc, ip);
+	if (!lockmode) {
+		struct xchk_dirent	save_de = {
+			.namelen	= name->len,
+			.ino		= ip->i_ino,
+		};
+
+		/* Couldn't lock the inode, so save the dirent for later. */
+		trace_xchk_dir_defer(sc->ip, name, ip->i_ino);
+
+		error = xfblob_storename(sd->dir_names, &save_de.name_cookie,
+				name);
+		if (!xchk_fblock_xref_process_error(sc, XFS_DATA_FORK, 0,
+					&error))
+			return error;
+
+		error = xfarray_append(sd->dir_entries, &save_de);
+		if (!xchk_fblock_xref_process_error(sc, XFS_DATA_FORK, 0,
+					&error))
+			return error;
+
+		return 0;
+	}
+
+	error = xchk_dir_parent_pointer(sd, name, ip);
+	xfs_iunlock(ip, lockmode);
+	return error;
+}
+
 /*
  * Scrub a single directory entry.
  *
@@ -80,6 +221,7 @@ xchk_dir_actor(
 {
 	struct xfs_mount	*mp = dp->i_mount;
 	struct xfs_inode	*ip;
+	struct xchk_dir		*sd = priv;
 	xfs_ino_t		lookup_ino;
 	xfs_dablk_t		offset;
 	int			error = 0;
@@ -146,6 +288,14 @@ xchk_dir_actor(
 		goto out;
 
 	xchk_dir_check_ftype(sc, offset, ip, name->type);
+
+	if (xfs_has_parent(mp)) {
+		error = xchk_dir_check_pptr_fast(sd, dapos, name, ip);
+		if (error)
+			goto out_rele;
+	}
+
+out_rele:
 	xchk_irele(sc, ip);
 out:
 	if (sc->sm->sm_flags & XFS_SCRUB_OFLAG_CORRUPT)
@@ -762,11 +912,148 @@ xchk_directory_blocks(
 	return error;
 }
 
+/*
+ * Revalidate a dirent that we collected in the past but couldn't check because
+ * of lock contention.  Returns 0 if the dirent is still valid, -ENOENT if it
+ * has gone away on us, or a negative errno.
+ */
+STATIC int
+xchk_dir_revalidate_dirent(
+	struct xchk_dir		*sd,
+	const struct xfs_name	*xname,
+	xfs_ino_t		ino)
+{
+	struct xfs_scrub	*sc = sd->sc;
+	xfs_ino_t		child_ino;
+	int			error;
+
+	/*
+	 * Look up the directory entry.  If we get -ENOENT, the directory entry
+	 * went away and there's nothing to revalidate.  Return any other
+	 * error.
+	 */
+	error = xchk_dir_lookup(sc, sc->ip, xname, &child_ino);
+	if (error)
+		return error;
+
+	/* The inode number changed, nothing to revalidate. */
+	if (ino != child_ino)
+		return -ENOENT;
+
+	return 0;
+}
+
+/*
+ * Check a directory entry's parent pointers the slow way, which means we cycle
+ * locks a bunch and put up with revalidation until we get it done.
+ */
+STATIC int
+xchk_dir_slow_dirent(
+	struct xchk_dir		*sd,
+	struct xchk_dirent	*dirent,
+	const struct xfs_name	*xname)
+{
+	struct xfs_scrub	*sc = sd->sc;
+	struct xfs_inode	*ip;
+	unsigned int		lockmode;
+	int			error;
+
+	/* Check that the deferred dirent still exists. */
+	if (sd->need_revalidate) {
+		error = xchk_dir_revalidate_dirent(sd, xname, dirent->ino);
+		if (error == -ENOENT)
+			return 0;
+		if (!xchk_fblock_xref_process_error(sc, XFS_DATA_FORK, 0,
+					&error))
+			return error;
+	}
+
+	error = xchk_iget(sc, dirent->ino, &ip);
+	if (error == -EINVAL || error == -ENOENT) {
+		xchk_fblock_set_corrupt(sc, XFS_DATA_FORK, 0);
+		return 0;
+	}
+	if (!xchk_fblock_xref_process_error(sc, XFS_DATA_FORK, 0, &error))
+		return error;
+
+	/*
+	 * If we can grab both IOLOCK and ILOCK of the alleged child, we can
+	 * proceed with the validation.
+	 */
+	lockmode = xchk_dir_lock_child(sc, ip);
+	if (lockmode) {
+		trace_xchk_dir_slowpath(sc->ip, xname, ip->i_ino);
+		goto check_pptr;
+	}
+
+	/*
+	 * We couldn't lock the child file.  Drop all the locks and try to
+	 * get them again, one at a time.
+	 */
+	xchk_iunlock(sc, sc->ilock_flags);
+	sd->need_revalidate = true;
+
+	trace_xchk_dir_ultraslowpath(sc->ip, xname, ip->i_ino);
+
+	error = xchk_dir_trylock_for_pptrs(sc, ip, &lockmode);
+	if (error)
+		goto out_rele;
+
+	/* Revalidate, since we just cycled the locks. */
+	error = xchk_dir_revalidate_dirent(sd, xname, dirent->ino);
+	if (error == -ENOENT) {
+		error = 0;
+		goto out_unlock;
+	}
+	if (!xchk_fblock_xref_process_error(sc, XFS_DATA_FORK, 0, &error))
+		goto out_unlock;
+
+check_pptr:
+	error = xchk_dir_parent_pointer(sd, xname, ip);
+out_unlock:
+	xfs_iunlock(ip, lockmode);
+out_rele:
+	xchk_irele(sc, ip);
+	return error;
+}
+
+/* Check all the dirents that we deferred the first time around. */
+STATIC int
+xchk_dir_finish_slow_dirents(
+	struct xchk_dir		*sd)
+{
+	xfarray_idx_t		array_cur;
+	int			error;
+
+	foreach_xfarray_idx(sd->dir_entries, array_cur) {
+		struct xchk_dirent	dirent;
+
+		if (sd->sc->sm->sm_flags & XFS_SCRUB_OFLAG_CORRUPT)
+			return 0;
+
+		error = xfarray_load(sd->dir_entries, array_cur, &dirent);
+		if (error)
+			return error;
+
+		error = xfblob_loadname(sd->dir_names, dirent.name_cookie,
+				&sd->xname, dirent.namelen);
+		if (error)
+			return error;
+
+		error = xchk_dir_slow_dirent(sd, &dirent, &sd->xname);
+		if (error)
+			return error;
+	}
+
+	return 0;
+}
+
 /* Scrub a whole directory. */
 int
 xchk_directory(
 	struct xfs_scrub	*sc)
 {
+	struct xchk_dir		*sd;
 	int			error;
 
 	if (!S_ISDIR(VFS_I(sc->ip)->i_mode))
@@ -799,9 +1086,60 @@ xchk_directory(
 	if (sc->sm->sm_flags & XFS_SCRUB_OFLAG_CORRUPT)
 		return 0;
 
+	sd = kvzalloc(sizeof(struct xchk_dir), XCHK_GFP_FLAGS);
+	if (!sd)
+		return -ENOMEM;
+	sd->sc = sc;
+	sd->xname.name = sd->namebuf;
+
+	if (xfs_has_parent(sc->mp)) {
+		char		*descr;
+
+		/*
+		 * Set up some staging memory for dirents that we can't check
+		 * due to locking contention.
+		 */
+		descr = xchk_xfile_ino_descr(sc, "slow directory entries");
+		error = xfarray_create(descr, 0, sizeof(struct xchk_dirent),
+				&sd->dir_entries);
+		kfree(descr);
+		if (error)
+			goto out_sd;
+
+		descr = xchk_xfile_ino_descr(sc, "slow directory entry names");
+		error = xfblob_create(descr, &sd->dir_names);
+		kfree(descr);
+		if (error)
+			goto out_entries;
+	}
+
 	/* Look up every name in this directory by hash. */
-	error = xchk_dir_walk(sc, sc->ip, xchk_dir_actor, NULL);
-	if (error && error != -ECANCELED)
+	error = xchk_dir_walk(sc, sc->ip, xchk_dir_actor, sd);
+	if (error == -ECANCELED)
+		error = 0;
+	if (error)
+		goto out_names;
+
+	if (xfs_has_parent(sc->mp)) {
+		error = xchk_dir_finish_slow_dirents(sd);
+		if (error == -ETIMEDOUT) {
+			/* Couldn't grab a lock, scrub was marked incomplete */
+			error = 0;
+			goto out_names;
+		}
+		if (error)
+			goto out_names;
+	}
+
+out_names:
+	if (sd->dir_names)
+		xfblob_destroy(sd->dir_names);
+out_entries:
+	if (sd->dir_entries)
+		xfarray_destroy(sd->dir_entries);
+out_sd:
+	kvfree(sd);
+	if (error)
 		return error;
 
 	/* If the dir is clean, it is clearly not zapped. */

fs/xfs/scrub/nlinks.c

@@ -18,6 +18,7 @@
 #include "xfs_dir2.h"
 #include "xfs_dir2_priv.h"
 #include "xfs_ag.h"
+#include "xfs_parent.h"
 #include "scrub/scrub.h"
 #include "scrub/common.h"
 #include "scrub/repair.h"
@@ -29,6 +30,7 @@
 #include "scrub/trace.h"
 #include "scrub/readdir.h"
 #include "scrub/tempfile.h"
+#include "scrub/listxattr.h"
 
 /*
  * Live Inode Link Count Checking
@@ -272,12 +274,17 @@ xchk_nlinks_collect_dirent(
 	 * number of parents of the root directory.
 	 *
 	 * Otherwise, increment the number of backrefs pointing back to ino.
+	 *
+	 * If the filesystem has parent pointers, we walk the pptrs to
+	 * determine the backref count.
 	 */
 	if (dotdot) {
 		if (dp == sc->mp->m_rootip)
 			error = xchk_nlinks_update_incore(xnc, ino, 1, 0, 0);
-		else
+		else if (!xfs_has_parent(sc->mp))
 			error = xchk_nlinks_update_incore(xnc, ino, 0, 1, 0);
+		else
+			error = 0;
 		if (error)
 			goto out_unlock;
 	}
@@ -314,6 +321,61 @@ xchk_nlinks_collect_dirent(
 	return error;
 }
 
+/* Bump the backref count for the inode referenced by this parent pointer. */
+STATIC int
+xchk_nlinks_collect_pptr(
+	struct xfs_scrub		*sc,
+	struct xfs_inode		*ip,
+	unsigned int			attr_flags,
+	const unsigned char		*name,
+	unsigned int			namelen,
+	const void			*value,
+	unsigned int			valuelen,
+	void				*priv)
+{
+	struct xfs_name			xname = {
+		.name			= name,
+		.len			= namelen,
+	};
+	struct xchk_nlink_ctrs		*xnc = priv;
+	const struct xfs_parent_rec	*pptr_rec = value;
+	xfs_ino_t			parent_ino;
+	int				error;
+
+	/* Update the shadow link counts if we haven't already failed. */
+
+	if (xchk_iscan_aborted(&xnc->collect_iscan)) {
+		error = -ECANCELED;
+		goto out_incomplete;
+	}
+
+	if (!(attr_flags & XFS_ATTR_PARENT))
+		return 0;
+
+	error = xfs_parent_from_attr(sc->mp, attr_flags, name, namelen, value,
+			valuelen, &parent_ino, NULL);
+	if (error)
+		return error;
+
+	trace_xchk_nlinks_collect_pptr(sc->mp, ip, &xname, pptr_rec);
+
+	mutex_lock(&xnc->lock);
+
+	error = xchk_nlinks_update_incore(xnc, parent_ino, 0, 1, 0);
+	if (error)
+		goto out_unlock;
+
+	mutex_unlock(&xnc->lock);
+	return 0;
+
+out_unlock:
+	mutex_unlock(&xnc->lock);
+	xchk_iscan_abort(&xnc->collect_iscan);
+out_incomplete:
+	xchk_set_incomplete(sc);
+	return error;
+}
+
 /* Walk a directory to bump the observed link counts of the children. */
 STATIC int
 xchk_nlinks_collect_dir(
@@ -360,6 +422,27 @@ xchk_nlinks_collect_dir(
 	if (error)
 		goto out_abort;
 
+	/* Walk the parent pointers to get real backref counts. */
+	if (xfs_has_parent(sc->mp)) {
+		/*
+		 * If the extended attributes look as though they has been
+		 * zapped by the inode record repair code, we cannot scan for
+		 * parent pointers.
+		 */
+		if (xchk_pptr_looks_zapped(dp)) {
+			error = -EBUSY;
+			goto out_unlock;
+		}
+
+		error = xchk_xattr_walk(sc, dp, xchk_nlinks_collect_pptr, xnc);
+		if (error == -ECANCELED) {
+			error = 0;
+			goto out_unlock;
+		}
+		if (error)
+			goto out_abort;
+	}
+
 	xchk_iscan_mark_visited(&xnc->collect_iscan, dp);
 	goto out_unlock;
 

fs/xfs/scrub/nlinks_repair.c

@@ -18,6 +18,8 @@
 #include "xfs_ialloc.h"
 #include "xfs_sb.h"
 #include "xfs_ag.h"
+#include "xfs_dir2.h"
+#include "xfs_parent.h"
 #include "scrub/scrub.h"
 #include "scrub/common.h"
 #include "scrub/repair.h"

fs/xfs/scrub/readdir.c

@@ -18,6 +18,7 @@
 #include "xfs_trans.h"
 #include "xfs_error.h"
 #include "scrub/scrub.h"
+#include "scrub/common.h"
 #include "scrub/readdir.h"
 
 /* Call a function for every entry in a shortform directory. */
@@ -380,3 +381,80 @@ xchk_dir_lookup(
 		*ino = args.inumber;
 	return error;
 }
+
+/*
+ * Try to grab the IOLOCK and ILOCK of sc->ip and ip, returning @ip's lock
+ * state.  The caller may have a transaction, so we must use trylock for both
+ * IOLOCKs.
+ */
+static inline unsigned int
+xchk_dir_trylock_both(
+	struct xfs_scrub	*sc,
+	struct xfs_inode	*ip)
+{
+	if (!xchk_ilock_nowait(sc, XFS_IOLOCK_EXCL))
+		return 0;
+
+	if (!xfs_ilock_nowait(ip, XFS_IOLOCK_SHARED))
+		goto parent_iolock;
+
+	xchk_ilock(sc, XFS_ILOCK_EXCL);
+	if (!xfs_ilock_nowait(ip, XFS_ILOCK_EXCL))
+		goto parent_ilock;
+
+	return XFS_IOLOCK_SHARED | XFS_ILOCK_EXCL;
+
+parent_ilock:
+	xchk_iunlock(sc, XFS_ILOCK_EXCL);
+	xfs_iunlock(ip, XFS_IOLOCK_SHARED);
+parent_iolock:
+	xchk_iunlock(sc, XFS_IOLOCK_EXCL);
+	return 0;
+}
+
+/*
+ * Try for a limited time to grab the IOLOCK and ILOCK of both the scrub target
+ * (@sc->ip) and the inode at the other end (@ip) of a directory or parent
+ * pointer link so that we can check that link.
+ *
+ * We do not know ahead of time that the directory tree is /not/ corrupt, so we
+ * cannot use the "lock two inode" functions because we do not know that there
+ * is not a racing thread trying to take the locks in opposite order.  First
+ * take IOLOCK_EXCL of the scrub target, and then try to take IOLOCK_SHARED
+ * of @ip to synchronize with the VFS.  Next, take ILOCK_EXCL of the scrub
+ * target and @ip to synchronize with XFS.
+ *
+ * If the trylocks succeed, *lockmode will be set to the locks held for @ip;
+ * @sc->ilock_flags will be set for the locks held for @sc->ip; and zero will
+ * be returned.  If not, returns -EDEADLOCK to try again; or -ETIMEDOUT if
+ * XCHK_TRY_HARDER was set.  Returns -EINTR if the process has been killed.
+ */
+int
+xchk_dir_trylock_for_pptrs(
+	struct xfs_scrub	*sc,
+	struct xfs_inode	*ip,
+	unsigned int		*lockmode)
+{
+	unsigned int		nr;
+	int			error = 0;
+
+	ASSERT(sc->ilock_flags == 0);
+
+	for (nr = 0; nr < HZ; nr++) {
+		*lockmode = xchk_dir_trylock_both(sc, ip);
+		if (*lockmode)
+			return 0;
+
+		if (xchk_should_terminate(sc, &error))
+			return error;
+
+		delay(1);
+	}
+
+	if (sc->flags & XCHK_TRY_HARDER) {
+		xchk_set_incomplete(sc);
+		return -ETIMEDOUT;
+	}
+
+	return -EDEADLOCK;
+}

fs/xfs/scrub/readdir.h

@@ -16,4 +16,7 @@ int xchk_dir_walk(struct xfs_scrub *sc, struct xfs_inode *dp,
 int xchk_dir_lookup(struct xfs_scrub *sc, struct xfs_inode *dp,
 		const struct xfs_name *name, xfs_ino_t *ino);
 
+int xchk_dir_trylock_for_pptrs(struct xfs_scrub *sc, struct xfs_inode *ip,
+		unsigned int *lockmode);
+
 #endif /* __XFS_SCRUB_READDIR_H__ */

fs/xfs/scrub/trace.c

@@ -19,6 +19,7 @@
 #include "xfs_da_format.h"
 #include "xfs_dir2.h"
 #include "xfs_rmap.h"
+#include "xfs_parent.h"
 #include "scrub/scrub.h"
 #include "scrub/xfile.h"
 #include "scrub/xfarray.h"

fs/xfs/scrub/trace.h

@@ -26,6 +26,7 @@ struct xchk_iscan;
 struct xchk_nlink;
 struct xchk_fscounters;
 struct xfs_rmap_update_params;
+struct xfs_parent_rec;
 
 /*
  * ftrace's __print_symbolic requires that all enum values be wrapped in the
@@ -1363,6 +1364,33 @@ TRACE_EVENT(xchk_nlinks_collect_dirent,
 		  __get_str(name))
 );
 
+TRACE_EVENT(xchk_nlinks_collect_pptr,
+	TP_PROTO(struct xfs_mount *mp, struct xfs_inode *dp,
+		 const struct xfs_name *name,
+		 const struct xfs_parent_rec *pptr),
+	TP_ARGS(mp, dp, name, pptr),
+	TP_STRUCT__entry(
+		__field(dev_t, dev)
+		__field(xfs_ino_t, dir)
+		__field(xfs_ino_t, ino)
+		__field(unsigned int, namelen)
+		__dynamic_array(char, name, name->len)
+	),
+	TP_fast_assign(
+		__entry->dev = mp->m_super->s_dev;
+		__entry->dir = dp->i_ino;
+		__entry->ino = be64_to_cpu(pptr->p_ino);
+		__entry->namelen = name->len;
+		memcpy(__get_str(name), name->name, name->len);
+	),
+	TP_printk("dev %d:%d dir 0x%llx -> ino 0x%llx name '%.*s'",
+		  MAJOR(__entry->dev), MINOR(__entry->dev),
+		  __entry->dir,
+		  __entry->ino,
+		  __entry->namelen,
+		  __get_str(name))
+);
+
 TRACE_EVENT(xchk_nlinks_collect_metafile,
 	TP_PROTO(struct xfs_mount *mp, xfs_ino_t ino),
 	TP_ARGS(mp, ino),
@@ -1511,6 +1539,43 @@ DEFINE_EVENT(xchk_nlinks_diff_class, name, \
 	TP_ARGS(mp, ip, live))
 DEFINE_SCRUB_NLINKS_DIFF_EVENT(xchk_nlinks_compare_inode);
 
+DECLARE_EVENT_CLASS(xchk_pptr_class,
+	TP_PROTO(struct xfs_inode *ip, const struct xfs_name *name,
+		 xfs_ino_t far_ino),
+	TP_ARGS(ip, name, far_ino),
+	TP_STRUCT__entry(
+		__field(dev_t, dev)
+		__field(xfs_ino_t, ino)
+		__field(unsigned int, namelen)
+		__dynamic_array(char, name, name->len)
+		__field(xfs_ino_t, far_ino)
+	),
+	TP_fast_assign(
+		__entry->dev = ip->i_mount->m_super->s_dev;
+		__entry->ino = ip->i_ino;
+		__entry->namelen = name->len;
+		memcpy(__get_str(name), name, name->len);
+		__entry->far_ino = far_ino;
+	),
+	TP_printk("dev %d:%d ino 0x%llx name '%.*s' far_ino 0x%llx",
+		  MAJOR(__entry->dev), MINOR(__entry->dev),
+		  __entry->ino,
+		  __entry->namelen,
+		  __get_str(name),
+		  __entry->far_ino)
+)
+#define DEFINE_XCHK_PPTR_EVENT(name) \
+DEFINE_EVENT(xchk_pptr_class, name, \
+	TP_PROTO(struct xfs_inode *ip, const struct xfs_name *name, \
+		 xfs_ino_t far_ino), \
+	TP_ARGS(ip, name, far_ino))
+DEFINE_XCHK_PPTR_EVENT(xchk_dir_defer);
+DEFINE_XCHK_PPTR_EVENT(xchk_dir_slowpath);
+DEFINE_XCHK_PPTR_EVENT(xchk_dir_ultraslowpath);
+DEFINE_XCHK_PPTR_EVENT(xchk_parent_defer);
+DEFINE_XCHK_PPTR_EVENT(xchk_parent_slowpath);
+DEFINE_XCHK_PPTR_EVENT(xchk_parent_ultraslowpath);
+
 /* repair tracepoints */
 #if IS_ENABLED(CONFIG_XFS_ONLINE_REPAIR)