Fix zil replay panic when TX_REMOVE followed by TX_CREATE

If TX_REMOVE is followed by TX_CREATE on the same object id, we need to
make sure the object removal is completely finished before creation. The
current implementation relies on dnode_hold_impl with
DNODE_MUST_BE_ALLOCATED returning ENOENT. While this check seems to work
fine before, in current version it does not guarantee the object removal
is completed.

We fix this by checking if DNODE_MUST_BE_FREE returns successful
instead. Also add test and remove dead code in dnode_hold_impl.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Tom Caputi <tcaputi@datto.com>
Signed-off-by: Chunwei Chen <david.chen@nutanix.com>
Closes #7151
Closes #8910
Closes #9123
Closes #9145

include/sys/dnode.h

@@ -46,6 +46,7 @@ extern "C" {
  */
 #define	DNODE_MUST_BE_ALLOCATED	1
 #define	DNODE_MUST_BE_FREE	2
+#define	DNODE_DRY_RUN		4
 
 /*
  * dnode_next_offset() flags.
@@ -415,6 +416,7 @@ int dnode_hold_impl(struct objset *dd, uint64_t object, int flag, int dn_slots,
 boolean_t dnode_add_ref(dnode_t *dn, void *ref);
 void dnode_rele(dnode_t *dn, void *ref);
 void dnode_rele_and_unlock(dnode_t *dn, void *tag, boolean_t evicting);
+int dnode_try_claim(objset_t *os, uint64_t object, int slots);
 void dnode_setdirty(dnode_t *dn, dmu_tx_t *tx);
 void dnode_sync(dnode_t *dn, dmu_tx_t *tx);
 void dnode_allocate(dnode_t *dn, dmu_object_type_t ot, int blocksize, int ibs,
@@ -531,11 +533,6 @@ typedef struct dnode_stats {
 	 * a range of dnode slots which would overflow the dnode_phys_t.
 	 */
 	kstat_named_t dnode_hold_free_overflow;
-	/*
-	 * Number of times a dnode_hold(...) was attempted on a dnode
-	 * which had already been unlinked in an earlier txg.
-	 */
-	kstat_named_t dnode_hold_free_txg;
 	/*
 	 * Number of times dnode_free_interior_slots() needed to retry
 	 * acquiring a slot zrl lock due to contention.

module/zfs/dnode.c

@@ -55,7 +55,6 @@ dnode_stats_t dnode_stats = {
 	{ "dnode_hold_free_lock_retry",		KSTAT_DATA_UINT64 },
 	{ "dnode_hold_free_overflow",		KSTAT_DATA_UINT64 },
 	{ "dnode_hold_free_refcount",		KSTAT_DATA_UINT64 },
-	{ "dnode_hold_free_txg",		KSTAT_DATA_UINT64 },
 	{ "dnode_free_interior_lock_retry",	KSTAT_DATA_UINT64 },
 	{ "dnode_allocate",			KSTAT_DATA_UINT64 },
 	{ "dnode_reallocate",			KSTAT_DATA_UINT64 },
@@ -1263,6 +1262,10 @@ dnode_buf_evict_async(void *dbu)
  * as an extra dnode slot by an large dnode, in which case it returns
  * ENOENT.
  *
+ * If the DNODE_DRY_RUN flag is set, we don't actually hold the dnode, just
+ * return whether the hold would succeed or not. tag and dnp should set to
+ * NULL in this case.
+ *
  * errors:
  * EINVAL - Invalid object number or flags.
  * ENOSPC - Hole too small to fulfill "slots" request (DNODE_MUST_BE_FREE)
@@ -1291,6 +1294,7 @@ dnode_hold_impl(objset_t *os, uint64_t object, int flag, int slots,
 
 	ASSERT(!(flag & DNODE_MUST_BE_ALLOCATED) || (slots == 0));
 	ASSERT(!(flag & DNODE_MUST_BE_FREE) || (slots > 0));
+	IMPLY(flag & DNODE_DRY_RUN, (tag == NULL) && (dnp == NULL));
 
 	/*
 	 * If you are holding the spa config lock as writer, you shouldn't
@@ -1320,8 +1324,11 @@ dnode_hold_impl(objset_t *os, uint64_t object, int flag, int slots,
 		if ((flag & DNODE_MUST_BE_FREE) && type != DMU_OT_NONE)
 			return (SET_ERROR(EEXIST));
 		DNODE_VERIFY(dn);
+		/* Don't actually hold if dry run, just return 0 */
+		if (!(flag & DNODE_DRY_RUN)) {
 			(void) zfs_refcount_add(&dn->dn_holds, tag);
 			*dnp = dn;
+		}
 		return (0);
 	}
 
@@ -1462,6 +1469,14 @@ dnode_hold_impl(objset_t *os, uint64_t object, int flag, int slots,
 			return (SET_ERROR(ENOENT));
 		}
 
+		/* Don't actually hold if dry run, just return 0 */
+		if (flag & DNODE_DRY_RUN) {
+			mutex_exit(&dn->dn_mtx);
+			dnode_slots_rele(dnc, idx, slots);
+			dbuf_rele(db, FTAG);
+			return (0);
+		}
+
 		DNODE_STAT_BUMP(dnode_hold_alloc_hits);
 	} else if (flag & DNODE_MUST_BE_FREE) {
 
@@ -1519,6 +1534,14 @@ dnode_hold_impl(objset_t *os, uint64_t object, int flag, int slots,
 			return (SET_ERROR(EEXIST));
 		}
 
+		/* Don't actually hold if dry run, just return 0 */
+		if (flag & DNODE_DRY_RUN) {
+			mutex_exit(&dn->dn_mtx);
+			dnode_slots_rele(dnc, idx, slots);
+			dbuf_rele(db, FTAG);
+			return (0);
+		}
+
 		dnode_set_slots(dnc, idx + 1, slots - 1, DN_SLOT_INTERIOR);
 		DNODE_STAT_BUMP(dnode_hold_free_hits);
 	} else {
@@ -1526,15 +1549,7 @@ dnode_hold_impl(objset_t *os, uint64_t object, int flag, int slots,
 		return (SET_ERROR(EINVAL));
 	}
 
-	if (dn->dn_free_txg) {
-		DNODE_STAT_BUMP(dnode_hold_free_txg);
-		type = dn->dn_type;
-		mutex_exit(&dn->dn_mtx);
-		dnode_slots_rele(dnc, idx, slots);
-		dbuf_rele(db, FTAG);
-		return (SET_ERROR((flag & DNODE_MUST_BE_ALLOCATED) ?
-		    ENOENT : EEXIST));
-	}
+	ASSERT0(dn->dn_free_txg);
 
 	if (zfs_refcount_add(&dn->dn_holds, tag) == 1)
 		dbuf_add_ref(db, dnh);
@@ -1625,6 +1640,16 @@ dnode_rele_and_unlock(dnode_t *dn, void *tag, boolean_t evicting)
 	}
 }
 
+/*
+ * Test whether we can create a dnode at the specified location.
+ */
+int
+dnode_try_claim(objset_t *os, uint64_t object, int slots)
+{
+	return (dnode_hold_impl(os, object, DNODE_MUST_BE_FREE | DNODE_DRY_RUN,
+	    slots, NULL, NULL));
+}
+
 void
 dnode_setdirty(dnode_t *dn, dmu_tx_t *tx)
 {

module/zfs/zfs_replay.c

@@ -337,8 +337,8 @@ zfs_replay_create_acl(void *arg1, void *arg2, boolean_t byteswap)
 	xva.xva_vattr.va_nblocks = lr->lr_gen;
 	xva.xva_vattr.va_fsid = dnodesize;
 
-	error = dmu_object_info(zfsvfs->z_os, lr->lr_foid, NULL);
-	if (error != ENOENT)
+	error = dnode_try_claim(zfsvfs->z_os, objid, dnodesize >> DNODE_SHIFT);
+	if (error)
 		goto bail;
 
 	if (lr->lr_common.lrc_txtype & TX_CI)
@@ -473,8 +473,8 @@ zfs_replay_create(void *arg1, void *arg2, boolean_t byteswap)
 	xva.xva_vattr.va_nblocks = lr->lr_gen;
 	xva.xva_vattr.va_fsid = dnodesize;
 
-	error = dmu_object_info(zfsvfs->z_os, objid, NULL);
-	if (error != ENOENT)
+	error = dnode_try_claim(zfsvfs->z_os, objid, dnodesize >> DNODE_SHIFT);
+	if (error)
 		goto out;
 
 	if (lr->lr_common.lrc_txtype & TX_CI)

tests/runfiles/linux.run

@@ -835,8 +835,8 @@ tags = ['functional', 'scrub_mirror']
 tests = ['slog_001_pos', 'slog_002_pos', 'slog_003_pos', 'slog_004_pos',
     'slog_005_pos', 'slog_006_pos', 'slog_007_pos', 'slog_008_neg',
     'slog_009_neg', 'slog_010_neg', 'slog_011_neg', 'slog_012_neg',
-    'slog_013_pos', 'slog_014_pos', 'slog_015_neg', 'slog_replay_fs',
-    'slog_replay_volume']
+    'slog_013_pos', 'slog_014_pos', 'slog_015_neg', 'slog_replay_fs_001',
+    'slog_replay_fs_002', 'slog_replay_volume']
 tags = ['functional', 'slog']
 
 [tests/functional/snapshot]

tests/zfs-tests/tests/functional/slog/Makefile.am

@@ -17,7 +17,8 @@ dist_pkgdata_SCRIPTS = \
 	slog_013_pos.ksh \
 	slog_014_pos.ksh \
 	slog_015_neg.ksh \
-	slog_replay_fs.ksh \
+	slog_replay_fs_001.ksh \
+	slog_replay_fs_002.ksh \
 	slog_replay_volume.ksh
 
 dist_pkgdata_DATA = \

tests/zfs-tests/tests/functional/slog/slog_replay_fs_002.ksh

@@ -0,0 +1,137 @@
+#!/bin/ksh -p
+#
+# CDDL HEADER START
+#
+# The contents of this file are subject to the terms of the
+# Common Development and Distribution License (the "License").
+# You may not use this file except in compliance with the License.
+#
+# You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
+# or http://www.opensolaris.org/os/licensing.
+# See the License for the specific language governing permissions
+# and limitations under the License.
+#
+# When distributing Covered Code, include this CDDL HEADER in each
+# file and include the License file at usr/src/OPENSOLARIS.LICENSE.
+# If applicable, add the following below this CDDL HEADER, with the
+# fields enclosed by brackets "[]" replaced with your own identifying
+# information: Portions Copyright [yyyy] [name of copyright owner]
+#
+# CDDL HEADER END
+#
+
+#
+# Copyright 2007 Sun Microsystems, Inc.  All rights reserved.
+# Use is subject to license terms.
+#
+
+. $STF_SUITE/tests/functional/slog/slog.kshlib
+
+#
+# DESCRIPTION:
+#	Verify slog replay correctly when TX_REMOVEs are followed by
+#	TX_CREATEs.
+#
+# STRATEGY:
+#	1. Create a file system (TESTFS) with a lot of files
+#	2. Freeze TESTFS
+#	3. Remove all files then create a lot of files
+#	4. Copy TESTFS to temporary location (TESTDIR/copy)
+#	5. Unmount filesystem
+#	   <at this stage TESTFS is empty again and unfrozen, and the
+#	   intent log contains a complete set of deltas to replay it>
+#	6. Remount TESTFS <which replays the intent log>
+#	7. Compare TESTFS against the TESTDIR/copy
+#
+
+verify_runnable "global"
+
+function cleanup_fs
+{
+	cleanup
+}
+
+log_assert "Replay of intent log succeeds."
+log_onexit cleanup_fs
+log_must setup
+
+#
+# 1. Create a file system (TESTFS) with a lot of files
+#
+log_must zpool create $TESTPOOL $VDEV log mirror $LDEV
+log_must zfs set compression=on $TESTPOOL
+log_must zfs create $TESTPOOL/$TESTFS
+
+# Prep for the test of TX_REMOVE followed by TX_CREATE
+dnsize=(legacy auto 1k 2k 4k 8k 16k)
+NFILES=200
+log_must mkdir /$TESTPOOL/$TESTFS/dir0
+log_must eval 'for i in $(seq $NFILES); do zfs set dnodesize=${dnsize[$RANDOM % ${#dnsize[@]}]} $TESTPOOL/$TESTFS; touch /$TESTPOOL/$TESTFS/dir0/file.$i; done'
+
+#
+# Reimport to reset dnode allocation pointer.
+# This is to make sure we will have TX_REMOVE and TX_CREATE on same id
+#
+log_must zpool export $TESTPOOL
+log_must zpool import -f -d $VDIR $TESTPOOL
+
+#
+# This dd command works around an issue where ZIL records aren't created
+# after freezing the pool unless a ZIL header already exists. Create a file
+# synchronously to force ZFS to write one out.
+#
+log_must dd if=/dev/zero of=/$TESTPOOL/$TESTFS/sync \
+    conv=fdatasync,fsync bs=1 count=1
+
+#
+# 2. Freeze TESTFS
+#
+log_must zpool freeze $TESTPOOL
+
+#
+# 3. Remove all files then create a lot of files
+#
+# TX_REMOVE followed by TX_CREATE
+log_must eval 'rm -f /$TESTPOOL/$TESTFS/dir0/*'
+log_must eval 'for i in $(seq $NFILES); do zfs set dnodesize=${dnsize[$RANDOM % ${#dnsize[@]}]} $TESTPOOL/$TESTFS; touch /$TESTPOOL/$TESTFS/dir0/file.$i; done'
+
+#
+# 4. Copy TESTFS to temporary location (TESTDIR/copy)
+#
+log_must mkdir -p $TESTDIR/copy
+log_must cp -a /$TESTPOOL/$TESTFS/* $TESTDIR/copy/
+
+#
+# 5. Unmount filesystem and export the pool
+#
+# At this stage TESTFS is empty again and frozen, the intent log contains
+# a complete set of deltas to replay.
+#
+log_must zfs unmount /$TESTPOOL/$TESTFS
+
+log_note "Verify transactions to replay:"
+log_must zdb -iv $TESTPOOL/$TESTFS
+
+log_must zpool export $TESTPOOL
+
+#
+# 6. Remount TESTFS <which replays the intent log>
+#
+# Import the pool to unfreeze it and claim log blocks.  It has to be
+# `zpool import -f` because we can't write a frozen pool's labels!
+#
+log_must zpool import -f -d $VDIR $TESTPOOL
+
+#
+# 7. Compare TESTFS against the TESTDIR/copy
+#
+log_note "Verify current block usage:"
+log_must zdb -bcv $TESTPOOL
+
+log_note "Verify number of files"
+log_must test "$(ls /$TESTPOOL/$TESTFS/dir0 | wc -l)" -eq $NFILES
+
+log_note "Verify working set diff:"
+log_must diff -r /$TESTPOOL/$TESTFS $TESTDIR/copy
+
+log_pass "Replay of intent log succeeds."