[PATCH 20/22] xfs: scrub parent pointers

Darrick J. Wong
2017-07-21T04:40:42Z

From: Darrick J. Wong <darrick.wong@oracle.com>

Scrub parent pointers, sort of. For directories, we can ride the
'..' entry up to the parent to confirm that there's at most one
dentry that points back to this directory.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---
fs/xfs/Makefile | 1
fs/xfs/libxfs/xfs_fs.h | 3 -
fs/xfs/scrub/common.c | 4 +
fs/xfs/scrub/common.h | 2
fs/xfs/scrub/parent.c | 252 ++++++++++++++++++++++++++++++++++++++++++++++++
5 files changed, 261 insertions(+), 1 deletion(-)
create mode 100644 fs/xfs/scrub/parent.c

diff --git a/fs/xfs/Makefile b/fs/xfs/Makefile
index 3d862b9..e73cdc2 100644
--- a/fs/xfs/Makefile
+++ b/fs/xfs/Makefile
@@ -151,6 +151,7 @@ xfs-y += $(addprefix scrub/, \
ialloc.o \
inode.o \
metabufs.o \
+ parent.o \
refcount.o \
rmap.o \
symlink.o \
diff --git a/fs/xfs/libxfs/xfs_fs.h b/fs/xfs/libxfs/xfs_fs.h
index 95d9ce9..4ad3056 100644
--- a/fs/xfs/libxfs/xfs_fs.h
+++ b/fs/xfs/libxfs/xfs_fs.h
@@ -500,7 +500,8 @@ struct xfs_scrub_metadata {
#define XFS_SCRUB_TYPE_DIR 16 /* directory */
#define XFS_SCRUB_TYPE_XATTR 17 /* extended attribute */
#define XFS_SCRUB_TYPE_SYMLINK 18 /* symbolic link */
-#define XFS_SCRUB_TYPE_MAX 18
+#define XFS_SCRUB_TYPE_PARENT 19 /* parent pointers */
+#define XFS_SCRUB_TYPE_MAX 19

/* i: repair this metadata */
#define XFS_SCRUB_FLAG_REPAIR (1 << 0)
diff --git a/fs/xfs/scrub/common.c b/fs/xfs/scrub/common.c
index 4003c2f..6f701c6 100644
--- a/fs/xfs/scrub/common.c
+++ b/fs/xfs/scrub/common.c
@@ -856,6 +856,10 @@ static const struct xfs_scrub_meta_fns meta_scrub_fns[] = {
.setup = xfs_scrub_setup_symlink,
.scrub = xfs_scrub_symlink,
},
+ { /* parent pointers */
+ .setup = xfs_scrub_setup_parent,
+ .scrub = xfs_scrub_parent,
+ },
};

/* Dispatch metadata scrubbing. */
diff --git a/fs/xfs/scrub/common.h b/fs/xfs/scrub/common.h
index 6d02a64..1873a31 100644
--- a/fs/xfs/scrub/common.h
+++ b/fs/xfs/scrub/common.h
@@ -223,6 +223,7 @@ SETUP_FN(xfs_scrub_setup_inode_bmap_data);
SETUP_FN(xfs_scrub_setup_inode_bmap);
SETUP_FN(xfs_scrub_setup_directory);
SETUP_FN(xfs_scrub_setup_xattr);
+SETUP_FN(xfs_scrub_setup_parent);
SETUP_FN(xfs_scrub_setup_symlink);
#undef SETUP_FN

@@ -247,6 +248,7 @@ SCRUB_FN(xfs_scrub_bmap_attr);
SCRUB_FN(xfs_scrub_bmap_cow);
SCRUB_FN(xfs_scrub_directory);
SCRUB_FN(xfs_scrub_xattr);
+SCRUB_FN(xfs_scrub_parent);
SCRUB_FN(xfs_scrub_symlink);
#undef SCRUB_FN

diff --git a/fs/xfs/scrub/parent.c b/fs/xfs/scrub/parent.c
new file mode 100644
index 0000000..e604885
--- /dev/null
+++ b/fs/xfs/scrub/parent.c
@@ -0,0 +1,252 @@
+/*
+ * Copyright (C) 2017 Oracle. All Rights Reserved.
+ *
+ * Author: Darrick J. Wong <darrick.wong@oracle.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it would be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA.
+ */
+#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_defer.h"
+#include "xfs_btree.h"
+#include "xfs_bit.h"
+#include "xfs_log_format.h"
+#include "xfs_trans.h"
+#include "xfs_trace.h"
+#include "xfs_sb.h"
+#include "xfs_inode.h"
+#include "xfs_icache.h"
+#include "xfs_dir2.h"
+#include "xfs_dir2_priv.h"
+#include "scrub/common.h"
+
+/* Set us up to scrub parents. */
+int
+xfs_scrub_setup_parent(
+ struct xfs_scrub_context *sc,
+ struct xfs_inode *ip)
+{
+ return xfs_scrub_setup_inode_contents(sc, ip, 0);
+}
+
+/* Parent pointers */
+
+/* Look for an entry in a parent pointing to this inode. */
+
+struct xfs_scrub_parent_ctx {
+ struct dir_context dc;
+ xfs_ino_t ino;
+ xfs_nlink_t nr;
+};
+
+/* Look for a single entry in a directory pointing to an inode. */
+STATIC int
+xfs_scrub_parent_actor(
+ struct dir_context *dc,
+ const char *name,
+ int namelen,
+ loff_t pos,
+ u64 ino,
+ unsigned type)
+{
+ struct xfs_scrub_parent_ctx *spc;
+
+ spc = container_of(dc, struct xfs_scrub_parent_ctx, dc);
+ if (spc->ino == ino)
+ spc->nr++;
+ return 0;
+}
+
+/* Count the number of dentries in the parent dir that point to this inode. */
+STATIC int
+xfs_scrub_parent_count_parent_dentries(
+ struct xfs_scrub_context *sc,
+ struct xfs_inode *parent,
+ xfs_nlink_t *nr)
+{
+ struct xfs_scrub_parent_ctx spc = {
+ .dc.actor = xfs_scrub_parent_actor,
+ .dc.pos = 0,
+ .ino = sc->ip->i_ino,
+ .nr = 0,
+ };
+ struct xfs_ifork *ifp;
+ size_t bufsize;
+ loff_t oldpos;
+ uint lock_mode;
+ int error;
+
+ /*
+ * Load the parent directory's extent map. A regular directory
+ * open would start readahead (and thus load the extent map)
+ * before we even got to a readdir call, but this isn't
+ * guaranteed here.
+ */
+ lock_mode = xfs_ilock_data_map_shared(parent);
+ ifp = XFS_IFORK_PTR(parent, XFS_DATA_FORK);
+ if (XFS_IFORK_FORMAT(parent, XFS_DATA_FORK) == XFS_DINODE_FMT_BTREE &&
+ !(ifp->if_flags & XFS_IFEXTENTS)) {
+ error = xfs_iread_extents(sc->tp, parent, XFS_DATA_FORK);
+ if (error) {
+ xfs_iunlock(parent, lock_mode);
+ return error;
+ }
+ }
+ xfs_iunlock(parent, lock_mode);
+
+ /*
+ * Iterate the parent dir to confirm that there is
+ * exactly one entry pointing back to the inode being
+ * scanned.
+ */
+ bufsize = (size_t)min_t(loff_t, 32768, parent->i_d.di_size);
+ oldpos = 0;
+ while (true) {
+ error = xfs_readdir(sc->tp, parent, &spc.dc, bufsize);
+ if (error)
+ goto out;
+ if (oldpos == spc.dc.pos)
+ break;
+ oldpos = spc.dc.pos;
+ }
+ *nr = spc.nr;
+out:
+ return error;
+}
+
+/* Scrub a parent pointer. */
+#define XFS_SCRUB_PARENT_CHECK(fs_ok) \
+ XFS_SCRUB_DATA_CHECK(sc, XFS_DATA_FORK, 0, "parent", fs_ok)
+#define XFS_SCRUB_PARENT_GOTO(fs_ok, label) \
+ XFS_SCRUB_DATA_GOTO(sc, XFS_DATA_FORK, 0, "parent", fs_ok, label)
+#define XFS_SCRUB_PARENT_OP_ERROR_GOTO(label) \
+ XFS_SCRUB_FILE_OP_ERROR_GOTO(sc, XFS_DATA_FORK, 0, "parent", \
+ &error, label)
+int
+xfs_scrub_parent(
+ struct xfs_scrub_context *sc)
+{
+ struct xfs_mount *mp = sc->mp;
+ struct xfs_inode *dp = NULL;
+ xfs_ino_t dnum;
+ xfs_nlink_t nr;
+ int tries = 0;
+ int error;
+
+ /*
+ * If we're a directory, check that the '..' link points up to
+ * a directory that has one entry pointing to us.
+ */
+ if (!S_ISDIR(VFS_I(sc->ip)->i_mode))
+ return -ENOENT;
+
+ /*
+ * The VFS grabs a read or write lock via i_rwsem before it reads
+ * or writes to a directory. If we've gotten this far we've
+ * already obtained IOLOCK_EXCL, which (since 4.10) is the same as
+ * getting a write lock on i_rwsem. Therefore, it is safe for us
+ * to drop the ILOCK here in order to do directory lookups.
+ */
+ sc->ilock_flags &= ~(XFS_ILOCK_EXCL | XFS_MMAPLOCK_EXCL);
+ xfs_iunlock(sc->ip, XFS_ILOCK_EXCL | XFS_MMAPLOCK_EXCL);
+
+ /* Look up '..' */
+ error = xfs_dir_lookup(sc->tp, sc->ip, &xfs_name_dotdot, &dnum, NULL);
+ XFS_SCRUB_PARENT_OP_ERROR_GOTO(out);
+
+ /* Is this the root dir? Then '..' must point to itself. */
+ if (sc->ip == mp->m_rootip) {
+ XFS_SCRUB_PARENT_CHECK(sc->ip->i_ino == mp->m_sb.sb_rootino);
+ XFS_SCRUB_PARENT_CHECK(dnum == sc->ip->i_ino);
+ return 0;
+ }
+
+try_again:
+ /* Otherwise, '..' must not point to ourselves. */
+ XFS_SCRUB_PARENT_GOTO(sc->ip->i_ino != dnum, out);
+
+ error = xfs_iget(mp, sc->tp, dnum, 0, 0, &dp);
+ XFS_SCRUB_PARENT_OP_ERROR_GOTO(out);
+ XFS_SCRUB_PARENT_GOTO(dp != sc->ip, out_rele);
+
+ /*
+ * We prefer to keep the inode locked while we lock and search
+ * its alleged parent for a forward reference. However, this
+ * child -> parent scheme can deadlock with the parent -> child
+ * scheme that is normally used. Therefore, if we can lock the
+ * parent, just validate the references and get out.
+ */
+ if (xfs_ilock_nowait(dp, XFS_IOLOCK_SHARED)) {
+ error = xfs_scrub_parent_count_parent_dentries(sc, dp, &nr);
+ XFS_SCRUB_PARENT_OP_ERROR_GOTO(out_unlock);
+ XFS_SCRUB_PARENT_CHECK(nr == 1);
+ goto out_unlock;
+ }
+
+ /*
+ * The game changes if we get here. We failed to lock the parent,
+ * so we're going to try to verify both pointers while only holding
+ * one lock so as to avoid deadlocking with something that's actually
+ * trying to traverse down the directory tree.
+ */
+ xfs_iunlock(sc->ip, sc->ilock_flags);
+ sc->ilock_flags = 0;
+ xfs_ilock(dp, XFS_IOLOCK_SHARED);
+
+ /* Go looking for our dentry. */
+ error = xfs_scrub_parent_count_parent_dentries(sc, dp, &nr);
+ XFS_SCRUB_PARENT_OP_ERROR_GOTO(out_unlock);
+
+ /* Drop the parent lock, relock this inode. */
+ xfs_iunlock(dp, XFS_IOLOCK_SHARED);
+ sc->ilock_flags = XFS_IOLOCK_EXCL;
+ xfs_ilock(sc->ip, sc->ilock_flags);
+
+ /* Look up '..' to see if the inode changed. */
+ error = xfs_dir_lookup(sc->tp, sc->ip, &xfs_name_dotdot, &dnum, NULL);
+ XFS_SCRUB_PARENT_OP_ERROR_GOTO(out_rele);
+
+ /* Drat, parent changed. Try again! */
+ if (dnum != dp->i_ino) {
+ IRELE(dp);
+ tries++;
+ if (tries < 20)
+ goto try_again;
+ XFS_SCRUB_INCOMPLETE(sc, "parent", false);
+ goto out;
+ }
+ IRELE(dp);
+
+ /*
+ * '..' didn't change, so check that there was only one entry
+ * for us in the parent.
+ */
+ XFS_SCRUB_PARENT_CHECK(nr == 1);
+ goto out;
+
+out_unlock:
+ xfs_iunlock(dp, XFS_IOLOCK_SHARED);
+out_rele:
+ IRELE(dp);
+out:
+ return error;
+}
+#undef XFS_SCRUB_PARENT_OP_ERROR_GOTO
+#undef XFS_SCRUB_PARENT_GOTO
+#undef XFS_SCRUB_PARENT_CHECK