xfs: teach online scrub to find directory tree structure problems

Create a new scrubber that detects corruptions within the directory tree
structure itself.  It can detect directories with multiple parents;
loops within the directory tree; and directory loops not accessible from
the root.

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

1 files changed, 795 insertions, 0 deletions

diff --git a/fs/xfs/scrub/dirtree.c b/fs/xfs/scrub/dirtree.c
new file mode 100644
index 000000000000..807c8a8ca7d4
--- /dev/null
+++ b/fs/xfs/scrub/dirtree.c
@@ -0,0 +1,795 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2023-2024 Oracle.  All Rights Reserved.
+ * Author: Darrick J. Wong <djwong@kernel.org>
+ */
+#include "xfs.h"
+#include "xfs_fs.h"
+#include "xfs_shared.h"
+#include "xfs_format.h"
+#include "xfs_trans_resv.h"
+#include "xfs_mount.h"
+#include "xfs_log_format.h"
+#include "xfs_trans.h"
+#include "xfs_inode.h"
+#include "xfs_icache.h"
+#include "xfs_dir2.h"
+#include "xfs_dir2_priv.h"
+#include "xfs_attr.h"
+#include "xfs_parent.h"
+#include "scrub/scrub.h"
+#include "scrub/common.h"
+#include "scrub/bitmap.h"
+#include "scrub/ino_bitmap.h"
+#include "scrub/xfile.h"
+#include "scrub/xfarray.h"
+#include "scrub/xfblob.h"
+#include "scrub/listxattr.h"
+#include "scrub/trace.h"
+#include "scrub/dirtree.h"
+
+/*
+ * Directory Tree Structure Validation
+ * ===================================
+ *
+ * Validating the tree qualities of the directory tree structure can be
+ * difficult.  If the tree is frozen, running a depth (or breadth) first search
+ * and marking a bitmap suffices to determine if there is a cycle.  XORing the
+ * mark bitmap with the inode bitmap afterwards tells us if there are
+ * disconnected cycles.  If the tree is not frozen, directory updates can move
+ * subtrees across the scanner wavefront, which complicates the design greatly.
+ *
+ * Directory parent pointers change that by enabling an incremental approach to
+ * validation of the tree structure.  Instead of using one thread to scan the
+ * entire filesystem, we instead can have multiple threads walking individual
+ * subdirectories upwards to the root.  In a perfect world, the IOLOCK would
+ * suffice to stabilize two directories in a parent -> child relationship.
+ * Unfortunately, the VFS does not take the IOLOCK when moving a child
+ * subdirectory, so we instead synchronize on ILOCK and use dirent update hooks
+ * to detect a race.  If a race occurs in a path, we restart the scan.
+ *
+ * If the walk terminates without reaching the root, we know the path is
+ * disconnected and ought to be attached to the lost and found.  If on the walk
+ * we find the same subdir that we're scanning, we know this is a cycle and
+ * should delete an incoming edge.  If we find multiple paths to the root, we
+ * know to delete an incoming edge.
+ *
+ * There are two big hitches with this approach: first, all file link counts
+ * must be correct to prevent other writers from doing the wrong thing with the
+ * directory tree structure.  Second, because we're walking upwards in a tree
+ * of arbitrary depth, we cannot hold all the ILOCKs.  Instead, we will use a
+ * directory update hook to invalidate the scan results if one of the paths
+ * we've scanned has changed.
+ */
+
+/* Clean up the dirtree checking resources. */
+STATIC void
+xchk_dirtree_buf_cleanup(
+	void			*buf)
+{
+	struct xchk_dirtree	*dl = buf;
+	struct xchk_dirpath	*path, *n;
+
+	xchk_dirtree_for_each_path_safe(dl, path, n) {
+		list_del_init(&path->list);
+		xino_bitmap_destroy(&path->seen_inodes);
+		kfree(path);
+	}
+
+	xfblob_destroy(dl->path_names);
+	xfarray_destroy(dl->path_steps);
+	mutex_destroy(&dl->lock);
+}
+
+/* Set us up to look for directory loops. */
+int
+xchk_setup_dirtree(
+	struct xfs_scrub	*sc)
+{
+	struct xchk_dirtree	*dl;
+	char			*descr;
+	int			error;
+
+	dl = kvzalloc(sizeof(struct xchk_dirtree), XCHK_GFP_FLAGS);
+	if (!dl)
+		return -ENOMEM;
+	dl->sc = sc;
+	dl->xname.name = dl->namebuf;
+	INIT_LIST_HEAD(&dl->path_list);
+	dl->root_ino = NULLFSINO;
+
+	mutex_init(&dl->lock);
+
+	descr = xchk_xfile_ino_descr(sc, "dirtree path steps");
+	error = xfarray_create(descr, 0, sizeof(struct xchk_dirpath_step),
+			&dl->path_steps);
+	kfree(descr);
+	if (error)
+		goto out_dl;
+
+	descr = xchk_xfile_ino_descr(sc, "dirtree path names");
+	error = xfblob_create(descr, &dl->path_names);
+	kfree(descr);
+	if (error)
+		goto out_steps;
+
+	error = xchk_setup_inode_contents(sc, 0);
+	if (error)
+		goto out_names;
+
+	sc->buf = dl;
+	sc->buf_cleanup = xchk_dirtree_buf_cleanup;
+	return 0;
+
+out_names:
+	xfblob_destroy(dl->path_names);
+out_steps:
+	xfarray_destroy(dl->path_steps);
+out_dl:
+	mutex_destroy(&dl->lock);
+	kvfree(dl);
+	return error;
+}
+
+/*
+ * Add the parent pointer described by @dl->pptr to the given path as a new
+ * step.  Returns -ELNRNG if the path is too deep.
+ */
+STATIC int
+xchk_dirpath_append(
+	struct xchk_dirtree		*dl,
+	struct xfs_inode		*ip,
+	struct xchk_dirpath		*path,
+	const struct xfs_name		*name,
+	const struct xfs_parent_rec	*pptr)
+{
+	struct xchk_dirpath_step	step = {
+		.pptr_rec		= *pptr, /* struct copy */
+		.name_len		= name->len,
+	};
+	int				error;
+
+	/*
+	 * If this path is more than 2 billion steps long, this directory tree
+	 * is too far gone to fix.
+	 */
+	if (path->nr_steps >= XFS_MAXLINK)
+		return -ELNRNG;
+
+	error = xfblob_storename(dl->path_names, &step.name_cookie, name);
+	if (error)
+		return error;
+
+	error = xino_bitmap_set(&path->seen_inodes, ip->i_ino);
+	if (error)
+		return error;
+
+	error = xfarray_append(dl->path_steps, &step);
+	if (error)
+		return error;
+
+	path->nr_steps++;
+	return 0;
+}
+
+/*
+ * Create an xchk_path for each parent pointer of the directory that we're
+ * scanning.  For each path created, we will eventually try to walk towards the
+ * root with the goal of deleting all parents except for one that leads to the
+ * root.
+ *
+ * Returns -EFSCORRUPTED to signal that the inode being scanned has a corrupt
+ * parent pointer and hence there's no point in continuing; or -ENOSR if there
+ * are too many parent pointers for this directory.
+ */
+STATIC int
+xchk_dirtree_create_path(
+	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_dirtree		*dl = priv;
+	struct xchk_dirpath		*path;
+	const struct xfs_parent_rec	*rec = value;
+	int				error;
+
+	if (!(attr_flags & XFS_ATTR_PARENT))
+		return 0;
+
+	error = xfs_parent_from_attr(sc->mp, attr_flags, name, namelen, value,
+			valuelen, NULL, NULL);
+	if (error)
+		return error;
+
+	/*
+	 * If there are more than 2 billion actual parent pointers for this
+	 * subdirectory, this fs is too far gone to fix.
+	 */
+	if (dl->nr_paths >= XFS_MAXLINK)
+		return -ENOSR;
+
+	trace_xchk_dirtree_create_path(sc, ip, dl->nr_paths, &xname, rec);
+
+	/*
+	 * Create a new xchk_path structure to remember this parent pointer
+	 * and record the first name step.
+	 */
+	path = kmalloc(sizeof(struct xchk_dirpath), XCHK_GFP_FLAGS);
+	if (!path)
+		return -ENOMEM;
+
+	INIT_LIST_HEAD(&path->list);
+	xino_bitmap_init(&path->seen_inodes);
+	path->nr_steps = 0;
+	path->outcome = XCHK_DIRPATH_SCANNING;
+
+	error = xchk_dirpath_append(dl, sc->ip, path, &xname, rec);
+	if (error)
+		goto out_path;
+
+	path->first_step = xfarray_length(dl->path_steps) - 1;
+	path->second_step = XFARRAY_NULLIDX;
+	path->path_nr = dl->nr_paths;
+
+	list_add_tail(&path->list, &dl->path_list);
+	dl->nr_paths++;
+	return 0;
+out_path:
+	kfree(path);
+	return error;
+}
+
+/*
+ * Validate that the first step of this path still has a corresponding
+ * parent pointer in @sc->ip.  We probably dropped @sc->ip's ILOCK while
+ * walking towards the roots, which is why this is necessary.
+ *
+ * This function has a side effect of loading the first parent pointer of this
+ * path into the parent pointer scratch pad.  This prepares us to walk up the
+ * directory tree towards the root.  Returns -ESTALE if the scan data is now
+ * out of date.
+ */
+STATIC int
+xchk_dirpath_revalidate(
+	struct xchk_dirtree		*dl,
+	struct xchk_dirpath		*path)
+{
+	struct xfs_scrub		*sc = dl->sc;
+	int				error;
+
+	/*
+	 * Look up the parent pointer that corresponds to the start of this
+	 * path.  If the parent pointer has disappeared on us, dump all the
+	 * scan results and try again.
+	 */
+	error = xfs_parent_lookup(sc->tp, sc->ip, &dl->xname, &dl->pptr_rec,
+			&dl->pptr_args);
+	if (error == -ENOATTR) {
+		trace_xchk_dirpath_disappeared(dl->sc, sc->ip, path->path_nr,
+				path->first_step, &dl->xname, &dl->pptr_rec);
+		dl->stale = true;
+		return -ESTALE;
+	}
+
+	return error;
+}
+
+/*
+ * Walk the parent pointers of a directory at the end of a path and record
+ * the parent that we find in @dl->xname/pptr_rec.
+ */
+STATIC int
+xchk_dirpath_find_next_step(
+	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 xchk_dirtree		*dl = priv;
+	const struct xfs_parent_rec	*rec = value;
+	int				error;
+
+	if (!(attr_flags & XFS_ATTR_PARENT))
+		return 0;
+
+	error = xfs_parent_from_attr(sc->mp, attr_flags, name, namelen, value,
+			valuelen, NULL, NULL);
+	if (error)
+		return error;
+
+	/*
+	 * If we've already set @dl->pptr_rec, then this directory has multiple
+	 * parents.  Signal this back to the caller via -EMLINK.
+	 */
+	if (dl->parents_found > 0)
+		return -EMLINK;
+
+	dl->parents_found++;
+	memcpy(dl->namebuf, name, namelen);
+	dl->xname.len = namelen;
+	dl->pptr_rec = *rec; /* struct copy */
+	return 0;
+}
+
+/* Set and log the outcome of a path walk. */
+static inline void
+xchk_dirpath_set_outcome(
+	struct xchk_dirtree		*dl,
+	struct xchk_dirpath		*path,
+	enum xchk_dirpath_outcome	outcome)
+{
+	trace_xchk_dirpath_set_outcome(dl->sc, path->path_nr, path->nr_steps,
+			outcome);
+
+	path->outcome = outcome;
+}
+
+/*
+ * Scan the directory at the end of this path for its parent directory link.
+ * If we find one, extend the path.  Returns -ESTALE if the scan data out of
+ * date.  Returns -EFSCORRUPTED if the parent pointer is bad; or -ELNRNG if
+ * the path got too deep.
+ */
+STATIC int
+xchk_dirpath_step_up(
+	struct xchk_dirtree	*dl,
+	struct xchk_dirpath	*path)
+{
+	struct xfs_scrub	*sc = dl->sc;
+	struct xfs_inode	*dp;
+	xfs_ino_t		parent_ino = be64_to_cpu(dl->pptr_rec.p_ino);
+	unsigned int		lock_mode;
+	int			error;
+
+	/* Grab and lock the parent directory. */
+	error = xchk_iget(sc, parent_ino, &dp);
+	if (error)
+		return error;
+
+	lock_mode = xfs_ilock_attr_map_shared(dp);
+	mutex_lock(&dl->lock);
+
+	if (dl->stale) {
+		error = -ESTALE;
+		goto out_scanlock;
+	}
+
+	/* We've reached the root directory; the path is ok. */
+	if (parent_ino == dl->root_ino) {
+		xchk_dirpath_set_outcome(dl, path, XCHK_DIRPATH_OK);
+		error = 0;
+		goto out_scanlock;
+	}
+
+	/*
+	 * The inode being scanned is its own distant ancestor!  Get rid of
+	 * this path.
+	 */
+	if (parent_ino == sc->ip->i_ino) {
+		xchk_dirpath_set_outcome(dl, path, XCHK_DIRPATH_DELETE);
+		error = 0;
+		goto out_scanlock;
+	}
+
+	/*
+	 * We've seen this inode before during the path walk.  There's a loop
+	 * above us in the directory tree.  This probably means that we cannot
+	 * continue, but let's keep walking paths to get a full picture.
+	 */
+	if (xino_bitmap_test(&path->seen_inodes, parent_ino)) {
+		xchk_dirpath_set_outcome(dl, path, XCHK_DIRPATH_LOOP);
+		error = 0;
+		goto out_scanlock;
+	}
+
+	/* The handle encoded in the parent pointer must match. */
+	if (VFS_I(dp)->i_generation != be32_to_cpu(dl->pptr_rec.p_gen)) {
+		trace_xchk_dirpath_badgen(dl->sc, dp, path->path_nr,
+				path->nr_steps, &dl->xname, &dl->pptr_rec);
+		error = -EFSCORRUPTED;
+		goto out_scanlock;
+	}
+
+	/* Parent pointer must point up to a directory. */
+	if (!S_ISDIR(VFS_I(dp)->i_mode)) {
+		trace_xchk_dirpath_nondir_parent(dl->sc, dp, path->path_nr,
+				path->nr_steps, &dl->xname, &dl->pptr_rec);
+		error = -EFSCORRUPTED;
+		goto out_scanlock;
+	}
+
+	/* Parent cannot be an unlinked directory. */
+	if (VFS_I(dp)->i_nlink == 0) {
+		trace_xchk_dirpath_unlinked_parent(dl->sc, dp, path->path_nr,
+				path->nr_steps, &dl->xname, &dl->pptr_rec);
+		error = -EFSCORRUPTED;
+		goto out_scanlock;
+	}
+
+	/*
+	 * 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;
+		xchk_set_incomplete(sc);
+		goto out_scanlock;
+	}
+
+	/*
+	 * Walk the parent pointers of @dp to find the parent of this directory
+	 * to find the next step in our walk.  If we find that @dp has exactly
+	 * one parent, the parent pointer information will be stored in
+	 * @dl->pptr_rec.  This prepares us for the next step of the walk.
+	 */
+	mutex_unlock(&dl->lock);
+	dl->parents_found = 0;
+	error = xchk_xattr_walk(sc, dp, xchk_dirpath_find_next_step, NULL, dl);
+	mutex_lock(&dl->lock);
+	if (error == -EFSCORRUPTED || error == -EMLINK ||
+	    (!error && dl->parents_found == 0)) {
+		/*
+		 * Further up the directory tree from @sc->ip, we found a
+		 * corrupt parent pointer, multiple parent pointers while
+		 * finding this directory's parent, or zero parents despite
+		 * having a nonzero link count.  Keep looking for other paths.
+		 */
+		xchk_dirpath_set_outcome(dl, path, XCHK_DIRPATH_CORRUPT);
+		error = 0;
+		goto out_scanlock;
+	}
+	if (error)
+		goto out_scanlock;
+
+	if (dl->stale) {
+		error = -ESTALE;
+		goto out_scanlock;
+	}
+
+	trace_xchk_dirpath_found_next_step(sc, dp, path->path_nr,
+			path->nr_steps, &dl->xname, &dl->pptr_rec);
+
+	/* Append to the path steps */
+	error = xchk_dirpath_append(dl, dp, path, &dl->xname, &dl->pptr_rec);
+	if (error)
+		goto out_scanlock;
+
+	if (path->second_step == XFARRAY_NULLIDX)
+		path->second_step = xfarray_length(dl->path_steps) - 1;
+
+out_scanlock:
+	mutex_unlock(&dl->lock);
+	xfs_iunlock(dp, lock_mode);
+	xchk_irele(sc, dp);
+	return error;
+}
+
+/*
+ * Walk the directory tree upwards towards what is hopefully the root
+ * directory, recording path steps as we go.  The current path components are
+ * stored in dl->pptr_rec and dl->xname.
+ *
+ * Returns -ESTALE if the scan data are out of date.  Returns -EFSCORRUPTED
+ * only if the direct parent pointer of @sc->ip associated with this path is
+ * corrupt.
+ */
+STATIC int
+xchk_dirpath_walk_upwards(
+	struct xchk_dirtree	*dl,
+	struct xchk_dirpath	*path)
+{
+	struct xfs_scrub	*sc = dl->sc;
+	int			error;
+
+	ASSERT(sc->ilock_flags & XFS_ILOCK_EXCL);
+
+	/* Reload the start of this path and make sure it's still there. */
+	error = xchk_dirpath_revalidate(dl, path);
+	if (error)
+		return error;
+
+	trace_xchk_dirpath_walk_upwards(sc, sc->ip, path->path_nr, &dl->xname,
+			&dl->pptr_rec);
+
+	/*
+	 * The inode being scanned is its own direct ancestor!
+	 * Get rid of this path.
+	 */
+	if (be64_to_cpu(dl->pptr_rec.p_ino) == sc->ip->i_ino) {
+		xchk_dirpath_set_outcome(dl, path, XCHK_DIRPATH_DELETE);
+		return 0;
+	}
+
+	/*
+	 * Drop ILOCK_EXCL on the inode being scanned.  We still hold
+	 * IOLOCK_EXCL on it, so it cannot move around or be renamed.
+	 *
+	 * Beyond this point we're walking up the directory tree, which means
+	 * that we can acquire and drop the ILOCK on an alias of sc->ip.  The
+	 * ILOCK state is no longer tracked in the scrub context.  Hence we
+	 * must drop @sc->ip's ILOCK during the walk.
+	 */
+	mutex_unlock(&dl->lock);
+	xchk_iunlock(sc, XFS_ILOCK_EXCL);
+
+	/*
+	 * Take the first step in the walk towards the root by checking the
+	 * start of this path, which is a direct parent pointer of @sc->ip.
+	 * If we see any kind of error here (including corruptions), the parent
+	 * pointer of @sc->ip is corrupt.  Stop the whole scan.
+	 */
+	error = xchk_dirpath_step_up(dl, path);
+	if (error) {
+		xchk_ilock(sc, XFS_ILOCK_EXCL);
+		mutex_lock(&dl->lock);
+		return error;
+	}
+
+	/*
+	 * Take steps upward from the second step in this path towards the
+	 * root.  If we hit corruption errors here, there's a problem
+	 * *somewhere* in the path, but we don't need to stop scanning.
+	 */
+	while (!error && path->outcome == XCHK_DIRPATH_SCANNING)
+		error = xchk_dirpath_step_up(dl, path);
+
+	/* Retake the locks we had, mark paths, etc. */
+	xchk_ilock(sc, XFS_ILOCK_EXCL);
+	mutex_lock(&dl->lock);
+	if (error == -EFSCORRUPTED) {
+		xchk_dirpath_set_outcome(dl, path, XCHK_DIRPATH_CORRUPT);
+		error = 0;
+	}
+	if (!error && dl->stale)
+		return -ESTALE;
+	return error;
+}
+
+/* Delete all the collected path information. */
+STATIC void
+xchk_dirtree_reset(
+	void			*buf)
+{
+	struct xchk_dirtree	*dl = buf;
+	struct xchk_dirpath	*path, *n;
+
+	ASSERT(dl->sc->ilock_flags & XFS_ILOCK_EXCL);
+
+	xchk_dirtree_for_each_path_safe(dl, path, n) {
+		list_del_init(&path->list);
+		xino_bitmap_destroy(&path->seen_inodes);
+		kfree(path);
+	}
+	dl->nr_paths = 0;
+
+	xfarray_truncate(dl->path_steps);
+	xfblob_truncate(dl->path_names);
+
+	dl->stale = false;
+}
+
+/*
+ * Load the name/pptr from the first step in this path into @dl->pptr_rec and
+ * @dl->xname.
+ */
+STATIC int
+xchk_dirtree_load_path(
+	struct xchk_dirtree		*dl,
+	struct xchk_dirpath		*path)
+{
+	struct xchk_dirpath_step	step;
+	int				error;
+
+	error = xfarray_load(dl->path_steps, path->first_step, &step);
+	if (error)
+		return error;
+
+	error = xfblob_loadname(dl->path_names, step.name_cookie, &dl->xname,
+			step.name_len);
+	if (error)
+		return error;
+
+	dl->pptr_rec = step.pptr_rec; /* struct copy */
+	return 0;
+}
+
+/*
+ * For each parent pointer of this subdir, trace a path upwards towards the
+ * root directory and record what we find.  Returns 0 for success;
+ * -EFSCORRUPTED if walking the parent pointers of @sc->ip failed, -ELNRNG if a
+ * path was too deep; -ENOSR if there were too many parent pointers; or
+ * a negative errno.
+ */
+STATIC int
+xchk_dirtree_find_paths_to_root(
+	struct xchk_dirtree	*dl)
+{
+	struct xfs_scrub	*sc = dl->sc;
+	struct xchk_dirpath	*path;
+	int			error = 0;
+
+	do {
+		if (xchk_should_terminate(sc, &error))
+			return error;
+
+		xchk_dirtree_reset(dl);
+
+		/*
+		 * 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(sc->ip)) {
+			xchk_set_incomplete(sc);
+			return -EBUSY;
+		}
+
+		/*
+		 * Create path walk contexts for each parent of the directory
+		 * that is being scanned.  Directories are supposed to have
+		 * only one parent, but this is how we detect multiple parents.
+		 */
+		error = xchk_xattr_walk(sc, sc->ip, xchk_dirtree_create_path,
+				NULL, dl);
+		if (error)
+			return error;
+
+		xchk_dirtree_for_each_path(dl, path) {
+			/* Load path components into dl->pptr/xname */
+			error = xchk_dirtree_load_path(dl, path);
+			if (error)
+				return error;
+
+			/*
+			 * Try to walk up each path to the root.  This enables
+			 * us to find directory loops in ancestors, and the
+			 * like.
+			 */
+			error = xchk_dirpath_walk_upwards(dl, path);
+			if (error == -EFSCORRUPTED) {
+				/*
+				 * A parent pointer of @sc->ip is bad, don't
+				 * bother continuing.
+				 */
+				break;
+			}
+			if (error == -ESTALE) {
+				/* This had better be an invalidation. */
+				ASSERT(dl->stale);
+				break;
+			}
+			if (error)
+				return error;
+		}
+	} while (dl->stale);
+
+	return error;
+}
+
+/*
+ * Figure out what to do with the paths we tried to find.  Do not call this
+ * if the scan results are stale.
+ */
+STATIC void
+xchk_dirtree_evaluate(
+	struct xchk_dirtree		*dl,
+	struct xchk_dirtree_outcomes	*oc)
+{
+	struct xchk_dirpath		*path;
+
+	ASSERT(!dl->stale);
+
+	/* Scan the paths we have to decide what to do. */
+	memset(oc, 0, sizeof(struct xchk_dirtree_outcomes));
+	xchk_dirtree_for_each_path(dl, path) {
+		trace_xchk_dirpath_evaluate_path(dl->sc, path->path_nr,
+				path->nr_steps, path->outcome);
+
+		switch (path->outcome) {
+		case XCHK_DIRPATH_SCANNING:
+			/* shouldn't get here */
+			ASSERT(0);
+			break;
+		case XCHK_DIRPATH_DELETE:
+			/* This one is already going away. */
+			oc->bad++;
+			break;
+		case XCHK_DIRPATH_CORRUPT:
+		case XCHK_DIRPATH_LOOP:
+			/* Couldn't find the end of this path. */
+			oc->suspect++;
+			break;
+		case XCHK_DIRPATH_STALE:
+			/* shouldn't get here either */
+			ASSERT(0);
+			break;
+		case XCHK_DIRPATH_OK:
+			/* This path got all the way to the root. */
+			oc->good++;
+			break;
+		}
+	}
+
+	trace_xchk_dirtree_evaluate(dl, oc);
+}
+
+/* Look for directory loops. */
+int
+xchk_dirtree(
+	struct xfs_scrub		*sc)
+{
+	struct xchk_dirtree_outcomes	oc;
+	struct xchk_dirtree		*dl = sc->buf;
+	int				error;
+
+	/*
+	 * Nondirectories do not point downwards to other files, so they cannot
+	 * cause a cycle in the directory tree.
+	 */
+	if (!S_ISDIR(VFS_I(sc->ip)->i_mode))
+		return -ENOENT;
+
+	ASSERT(xfs_has_parent(sc->mp));
+
+	/* Find the root of the directory tree. */
+	dl->root_ino = sc->mp->m_rootip->i_ino;
+
+	trace_xchk_dirtree_start(sc->ip, sc->sm, 0);
+
+	mutex_lock(&dl->lock);
+
+	/* Trace each parent pointer's path to the root. */
+	error = xchk_dirtree_find_paths_to_root(dl);
+	if (error == -EFSCORRUPTED || error == -ELNRNG || error == -ENOSR) {
+		/*
+		 * Don't bother walking the paths if the xattr structure or the
+		 * parent pointers are corrupt; this scan cannot be completed
+		 * without full information.
+		 */
+		xchk_ino_xref_set_corrupt(sc, sc->ip->i_ino);
+		error = 0;
+		goto out_scanlock;
+	}
+	if (error == -EBUSY) {
+		/*
+		 * We couldn't scan some directory's parent pointers because
+		 * the attr fork looked like it had been zapped.  The
+		 * scan was marked incomplete, so no further error code
+		 * is necessary.
+		 */
+		error = 0;
+		goto out_scanlock;
+	}
+	if (error)
+		goto out_scanlock;
+
+	/* Assess what we found in our path evaluation. */
+	xchk_dirtree_evaluate(dl, &oc);
+	if (xchk_dirtree_parentless(dl)) {
+		if (oc.good || oc.bad || oc.suspect)
+			xchk_ino_set_corrupt(sc, sc->ip->i_ino);
+	} else {
+		if (oc.bad || oc.good + oc.suspect != 1)
+			xchk_ino_set_corrupt(sc, sc->ip->i_ino);
+		if (oc.suspect)
+			xchk_ino_xref_set_corrupt(sc, sc->ip->i_ino);
+	}
+
+out_scanlock:
+	mutex_unlock(&dl->lock);
+	trace_xchk_dirtree_done(sc->ip, sc->sm, error);
+	return error;
+}