1 files changed, 351 insertions, 0 deletions
diff --git a/fs/xfs/scrub/nlinks_repair.c b/fs/xfs/scrub/nlinks_repair.c
new file mode 100644
index 000000000000..4ebdee095428
--- /dev/null
+++ b/fs/xfs/scrub/nlinks_repair.c
@@ -0,0 +1,351 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2021-2024 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_bmap_util.h"
+#include "xfs_iwalk.h"
+#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"
+#include "scrub/xfile.h"
+#include "scrub/xfarray.h"
+#include "scrub/iscan.h"
+#include "scrub/orphanage.h"
+#include "scrub/nlinks.h"
+#include "scrub/trace.h"
+#include "scrub/tempfile.h"
+
+/*
+ * Live Inode Link Count Repair
+ * ============================
+ *
+ * Use the live inode link count information that we collected to replace the
+ * nlink values of the incore inodes.  A scrub->repair cycle should have left
+ * the live data and hooks active, so this is safe so long as we make sure the
+ * inode is locked.
+ */
+
+/* Set up to repair inode link counts. */
+int
+xrep_setup_nlinks(
+	struct xfs_scrub	*sc)
+{
+	return xrep_orphanage_try_create(sc);
+}
+
+/*
+ * Inodes that aren't the root directory or the orphanage, have a nonzero link
+ * count, and no observed parents should be moved to the orphanage.
+ */
+static inline bool
+xrep_nlinks_is_orphaned(
+	struct xfs_scrub	*sc,
+	struct xfs_inode	*ip,
+	unsigned int		actual_nlink,
+	const struct xchk_nlink	*obs)
+{
+	if (obs->parents != 0)
+		return false;
+	if (xchk_inode_is_dirtree_root(ip) || ip == sc->orphanage)
+		return false;
+	return actual_nlink != 0;
+}
+
+/* Remove an inode from the unlinked list. */
+STATIC int
+xrep_nlinks_iunlink_remove(
+	struct xfs_scrub	*sc)
+{
+	struct xfs_perag	*pag;
+	int			error;
+
+	pag = xfs_perag_get(sc->mp, XFS_INO_TO_AGNO(sc->mp, sc->ip->i_ino));
+	error = xfs_iunlink_remove(sc->tp, pag, sc->ip);
+	xfs_perag_put(pag);
+	return error;
+}
+
+/*
+ * Correct the link count of the given inode.  Because we have to grab locks
+ * and resources in a certain order, it's possible that this will be a no-op.
+ */
+STATIC int
+xrep_nlinks_repair_inode(
+	struct xchk_nlink_ctrs	*xnc)
+{
+	struct xchk_nlink	obs;
+	struct xfs_scrub	*sc = xnc->sc;
+	struct xfs_mount	*mp = sc->mp;
+	struct xfs_inode	*ip = sc->ip;
+	uint64_t		total_links;
+	uint64_t		actual_nlink;
+	bool			orphanage_available = false;
+	bool			dirty = false;
+	int			error;
+
+	/*
+	 * Ignore temporary files being used to stage repairs, since we assume
+	 * they're correct for non-directories, and the directory repair code
+	 * doesn't bump the link counts for the children.
+	 */
+	if (xrep_is_tempfile(ip))
+		return 0;
+
+	/*
+	 * If the filesystem has an orphanage attached to the scrub context,
+	 * prepare for a link count repair that could involve @ip being adopted
+	 * by the lost+found.
+	 */
+	if (xrep_orphanage_can_adopt(sc)) {
+		error = xrep_orphanage_iolock_two(sc);
+		if (error)
+			return error;
+
+		error = xrep_adoption_trans_alloc(sc, &xnc->adoption);
+		if (error) {
+			xchk_iunlock(sc, XFS_IOLOCK_EXCL);
+			xrep_orphanage_iunlock(sc, XFS_IOLOCK_EXCL);
+		} else {
+			orphanage_available = true;
+		}
+	}
+
+	/*
+	 * Either there is no orphanage or we couldn't allocate resources for
+	 * that kind of update.  Let's try again with only the resources we
+	 * need for a simple link count update, since that's much more common.
+	 */
+	if (!orphanage_available) {
+		xchk_ilock(sc, XFS_IOLOCK_EXCL);
+
+		error = xfs_trans_alloc(mp, &M_RES(mp)->tr_link, 0, 0, 0,
+				&sc->tp);
+		if (error) {
+			xchk_iunlock(sc, XFS_IOLOCK_EXCL);
+			return error;
+		}
+
+		xchk_ilock(sc, XFS_ILOCK_EXCL);
+		xfs_trans_ijoin(sc->tp, ip, 0);
+	}
+
+	mutex_lock(&xnc->lock);
+
+	if (xchk_iscan_aborted(&xnc->collect_iscan)) {
+		error = -ECANCELED;
+		goto out_scanlock;
+	}
+
+	error = xfarray_load_sparse(xnc->nlinks, ip->i_ino, &obs);
+	if (error)
+		goto out_scanlock;
+
+	/*
+	 * We're done accessing the shared scan data, so we can drop the lock.
+	 * We still hold @ip's ILOCK, so its link count cannot change.
+	 */
+	mutex_unlock(&xnc->lock);
+
+	total_links = xchk_nlink_total(ip, &obs);
+	actual_nlink = VFS_I(ip)->i_nlink;
+
+	/*
+	 * Non-directories cannot have directories pointing up to them.
+	 *
+	 * We previously set error to zero, but set it again because one static
+	 * checker author fears that programmers will fail to maintain this
+	 * invariant and built their tool to flag this as a security risk.  A
+	 * different tool author made their bot complain about the redundant
+	 * store.  This is a never-ending and stupid battle; both tools missed
+	 * *actual bugs* elsewhere; and I no longer care.
+	 */
+	if (!S_ISDIR(VFS_I(ip)->i_mode) && obs.children != 0) {
+		trace_xrep_nlinks_unfixable_inode(mp, ip, &obs);
+		error = 0;
+		goto out_trans;
+	}
+
+	/*
+	 * Decide if we're going to move this file to the orphanage, and fix
+	 * up the incore link counts if we are.
+	 */
+	if (orphanage_available &&
+	    xrep_nlinks_is_orphaned(sc, ip, actual_nlink, &obs)) {
+		/* Figure out what name we're going to use here. */
+		error = xrep_adoption_compute_name(&xnc->adoption, &xnc->xname);
+		if (error)
+			goto out_trans;
+
+		/*
+		 * Reattach this file to the directory tree by moving it to
+		 * the orphanage per the adoption parameters that we already
+		 * computed.
+		 */
+		error = xrep_adoption_move(&xnc->adoption);
+		if (error)
+			goto out_trans;
+
+		/*
+		 * Re-read the link counts since the reparenting will have
+		 * updated our scan info.
+		 */
+		mutex_lock(&xnc->lock);
+		error = xfarray_load_sparse(xnc->nlinks, ip->i_ino, &obs);
+		mutex_unlock(&xnc->lock);
+		if (error)
+			goto out_trans;
+
+		total_links = xchk_nlink_total(ip, &obs);
+		actual_nlink = VFS_I(ip)->i_nlink;
+		dirty = true;
+	}
+
+	/*
+	 * If this inode is linked from the directory tree and on the unlinked
+	 * list, remove it from the unlinked list.
+	 */
+	if (total_links > 0 && xfs_inode_on_unlinked_list(ip)) {
+		error = xrep_nlinks_iunlink_remove(sc);
+		if (error)
+			goto out_trans;
+		dirty = true;
+	}
+
+	/*
+	 * If this inode is not linked from the directory tree yet not on the
+	 * unlinked list, put it on the unlinked list.
+	 */
+	if (total_links == 0 && !xfs_inode_on_unlinked_list(ip)) {
+		error = xfs_iunlink(sc->tp, ip);
+		if (error)
+			goto out_trans;
+		dirty = true;
+	}
+
+	/* Commit the new link count if it changed. */
+	if (total_links != actual_nlink) {
+		trace_xrep_nlinks_update_inode(mp, ip, &obs);
+
+		set_nlink(VFS_I(ip), min_t(unsigned long long, total_links,
+					   XFS_NLINK_PINNED));
+		dirty = true;
+	}
+
+	if (!dirty) {
+		error = 0;
+		goto out_trans;
+	}
+
+	xfs_trans_log_inode(sc->tp, ip, XFS_ILOG_CORE);
+
+	error = xrep_trans_commit(sc);
+	goto out_unlock;
+
+out_scanlock:
+	mutex_unlock(&xnc->lock);
+out_trans:
+	xchk_trans_cancel(sc);
+out_unlock:
+	xchk_iunlock(sc, XFS_ILOCK_EXCL);
+	if (orphanage_available) {
+		xrep_orphanage_iunlock(sc, XFS_ILOCK_EXCL);
+		xrep_orphanage_iunlock(sc, XFS_IOLOCK_EXCL);
+	}
+	xchk_iunlock(sc, XFS_IOLOCK_EXCL);
+	return error;
+}
+
+/*
+ * Try to visit every inode in the filesystem for repairs.  Move on if we can't
+ * grab an inode, since we're still making forward progress.
+ */
+static int
+xrep_nlinks_iter(
+	struct xchk_nlink_ctrs	*xnc,
+	struct xfs_inode	**ipp)
+{
+	int			error;
+
+	do {
+		error = xchk_iscan_iter(&xnc->compare_iscan, ipp);
+	} while (error == -EBUSY);
+
+	return error;
+}
+
+/* Commit the new inode link counters. */
+int
+xrep_nlinks(
+	struct xfs_scrub	*sc)
+{
+	struct xchk_nlink_ctrs	*xnc = sc->buf;
+	int			error;
+
+	/*
+	 * We need ftype for an accurate count of the number of child
+	 * subdirectory links.  Child subdirectories with a back link (dotdot
+	 * entry) but no forward link are moved to the orphanage, so we cannot
+	 * repair the link count of the parent directory based on the back link
+	 * count alone.  Filesystems without ftype support are rare (old V4) so
+	 * we just skip out here.
+	 */
+	if (!xfs_has_ftype(sc->mp))
+		return -EOPNOTSUPP;
+
+	/*
+	 * Use the inobt to walk all allocated inodes to compare and fix the
+	 * link counts.  Retry iget every tenth of a second for up to 30
+	 * seconds -- even if repair misses a few inodes, we still try to fix
+	 * as many of them as we can.
+	 */
+	xchk_iscan_start(sc, 30000, 100, &xnc->compare_iscan);
+	ASSERT(sc->ip == NULL);
+
+	while ((error = xrep_nlinks_iter(xnc, &sc->ip)) == 1) {
+		/*
+		 * Commit the scrub transaction so that we can create repair
+		 * transactions with the correct reservations.
+		 */
+		xchk_trans_cancel(sc);
+
+		error = xrep_nlinks_repair_inode(xnc);
+		xchk_iscan_mark_visited(&xnc->compare_iscan, sc->ip);
+		xchk_irele(sc, sc->ip);
+		sc->ip = NULL;
+		if (error)
+			break;
+
+		if (xchk_should_terminate(sc, &error))
+			break;
+
+		/*
+		 * Create a new empty transaction so that we can advance the
+		 * iscan cursor without deadlocking if the inobt has a cycle.
+		 * We can only push the inactivation workqueues with an empty
+		 * transaction.
+		 */
+		error = xchk_trans_alloc_empty(sc);
+		if (error)
+			break;
+	}
+	xchk_iscan_iter_finish(&xnc->compare_iscan);
+	xchk_iscan_teardown(&xnc->compare_iscan);
+
+	return error;
+}