Fix range locking in ZIL commit codepath

Since OpenZFS 7578 (1b7c1e5) if we have a ZVOL with logbias=throughput
we will force WR_INDIRECT itxs in zvol_log_write() setting itx->itx_lr
offset and length to the offset and length of the BIO from
zvol_write()->zvol_log_write(): these offset and length are later used
to take a range lock in zillog->zl_get_data function: zvol_get_data().

Now suppose we have a ZVOL with blocksize=8K and push 4K writes to
offset 0: we will only be range-locking 0-4096. This means the
ASSERTion we make in dbuf_unoverride() is no longer valid because now
dmu_sync() is called from zilog's get_data functions holding a partial
lock on the dbuf.

Fix this by taking a range lock on the whole block in zvol_get_data().

Signed-off-by: loli10K <ezomori.nozomu@gmail.com>

cmd/ztest/ztest.c

@@ -2145,6 +2145,7 @@ ztest_get_data(void *arg, lr_write_t *lr, char *buf, zio_t *zio)
 	if (buf != NULL) {	/* immediate write */
 		zgd_private->z_rl = ztest_range_lock(zd, object, offset, size,
 		    RL_READER);
+		zgd->zgd_rl = zgd_private->z_rl->z_rl;
 
 		error = dmu_read(os, object, offset, size, buf,
 		    DMU_READ_NO_PREFETCH);
@@ -2160,6 +2161,7 @@ ztest_get_data(void *arg, lr_write_t *lr, char *buf, zio_t *zio)
 
 		zgd_private->z_rl = ztest_range_lock(zd, object, offset, size,
 		    RL_READER);
+		zgd->zgd_rl = zgd_private->z_rl->z_rl;
 
 		error = dmu_buf_hold(os, object, offset, zgd, &db,
 		    DMU_READ_NO_PREFETCH);

module/zfs/dmu.c

@@ -49,6 +49,7 @@
 #include <sys/zfeature.h>
 #include <sys/abd.h>
 #include <sys/trace_dmu.h>
+#include <sys/zfs_rlock.h>
 #ifdef _KERNEL
 #include <sys/vmsystm.h>
 #include <sys/zfs_znode.h>
@@ -1815,6 +1816,11 @@ dmu_sync(zio_t *pio, uint64_t txg, dmu_sync_cb_t *done, zgd_t *zgd)
 	ASSERT(pio != NULL);
 	ASSERT(txg != 0);
 
+	/* dbuf is within the locked range */
+	ASSERT3U(db->db.db_offset, >=, zgd->zgd_rl->r_off);
+	ASSERT3U(db->db.db_offset + db->db.db_size, <=,
+	    zgd->zgd_rl->r_off + zgd->zgd_rl->r_len);
+
 	SET_BOOKMARK(&zb, ds->ds_object,
 	    db->db.db_object, db->db_level, db->db_blkid);
 

module/zfs/zfs_vnops.c

@@ -1050,7 +1050,7 @@ zfs_get_data(void *arg, lr_write_t *lr, char *buf, zio_t *zio)
 	} else { /* indirect write */
 		/*
 		 * Have to lock the whole block to ensure when it's
-		 * written out and it's checksum is being calculated
+		 * written out and its checksum is being calculated
 		 * that no one can change the data. We need to re-check
 		 * blocksize after we get the lock in case it's changed!
 		 */

module/zfs/zvol.c

@@ -821,6 +821,7 @@ zvol_discard(void *arg)
 	uint64_t start = BIO_BI_SECTOR(bio) << 9;
 	uint64_t size = BIO_BI_SIZE(bio);
 	uint64_t end = start + size;
+	boolean_t sync;
 	int error = 0;
 	dmu_tx_t *tx;
 	unsigned long start_jif;
@@ -830,9 +831,11 @@ zvol_discard(void *arg)
 	start_jif = jiffies;
 	generic_start_io_acct(WRITE, bio_sectors(bio), &zv->zv_disk->part0);
 
+	sync = bio_is_fua(bio) || zv->zv_objset->os_sync == ZFS_SYNC_ALWAYS;
+
 	if (end > zv->zv_volsize) {
 		error = SET_ERROR(EIO);
-		goto out;
+		goto unlock;
 	}
 
 	/*
@@ -848,7 +851,7 @@ zvol_discard(void *arg)
 	}
 
 	if (start >= end)
-		goto out;
+		goto unlock;
 
 	tx = dmu_tx_create(zv->zv_objset);
 	dmu_tx_mark_netfree(tx);
@@ -861,9 +864,11 @@ zvol_discard(void *arg)
 		error = dmu_free_long_range(zv->zv_objset,
 		    ZVOL_OBJ, start, size);
 	}
-
-out:
+unlock:
 	zfs_range_unlock(zvr->rl);
+	if (error == 0 && sync)
+		zil_commit(zv->zv_zilog, ZVOL_OBJ);
+
 	rw_exit(&zv->zv_suspend_lock);
 	generic_end_io_acct(WRITE, &zv->zv_disk->part0, start_jif);
 	BIO_END_IO(bio, -error);
@@ -933,6 +938,8 @@ zvol_request(struct request_queue *q, struct bio *bio)
 	}
 
 	if (rw == WRITE) {
+		boolean_t need_sync = B_FALSE;
+
 		if (unlikely(zv->zv_flags & ZVOL_RDONLY)) {
 			BIO_END_IO(bio, -SET_ERROR(EROFS));
 			goto out;
@@ -966,13 +973,24 @@ zvol_request(struct request_queue *q, struct bio *bio)
 		 */
 		zvr->rl = zfs_range_lock(&zv->zv_range_lock, offset, size,
 		    RL_WRITER);
+		/*
+		 * Sync writes and discards execute zil_commit() which may need
+		 * to take a RL_READER lock on the whole block being modified
+		 * via its zillog->zl_get_data(): to avoid circular dependency
+		 * issues with taskq threads execute these requests
+		 * synchronously here in zvol_request().
+		 */
+		need_sync = bio_is_fua(bio) ||
+		    zv->zv_objset->os_sync == ZFS_SYNC_ALWAYS;
 		if (bio_is_discard(bio) || bio_is_secure_erase(bio)) {
-			if (zvol_request_sync || taskq_dispatch(zvol_taskq,
-			    zvol_discard, zvr, TQ_SLEEP) == TASKQID_INVALID)
+			if (zvol_request_sync || need_sync ||
+			    taskq_dispatch(zvol_taskq, zvol_discard, zvr,
+			    TQ_SLEEP) == TASKQID_INVALID)
 				zvol_discard(zvr);
 		} else {
-			if (zvol_request_sync || taskq_dispatch(zvol_taskq,
-			    zvol_write, zvr, TQ_SLEEP) == TASKQID_INVALID)
+			if (zvol_request_sync || need_sync ||
+			    taskq_dispatch(zvol_taskq, zvol_write, zvr,
+			    TQ_SLEEP) == TASKQID_INVALID)
 				zvol_write(zvr);
 		}
 	} else {
@@ -1030,8 +1048,6 @@ zvol_get_data(void *arg, lr_write_t *lr, char *buf, zio_t *zio)
 
 	zgd = (zgd_t *)kmem_zalloc(sizeof (zgd_t), KM_SLEEP);
 	zgd->zgd_zilog = zv->zv_zilog;
-	zgd->zgd_rl = zfs_range_lock(&zv->zv_range_lock, offset, size,
-	    RL_READER);
 
 	/*
 	 * Write records come in two flavors: immediate and indirect.
@@ -1041,11 +1057,21 @@ zvol_get_data(void *arg, lr_write_t *lr, char *buf, zio_t *zio)
 	 * we don't have to write the data twice.
 	 */
 	if (buf != NULL) { /* immediate write */
+		zgd->zgd_rl = zfs_range_lock(&zv->zv_range_lock, offset, size,
+		    RL_READER);
 		error = dmu_read_by_dnode(zv->zv_dn, offset, size, buf,
 		    DMU_READ_NO_PREFETCH);
-	} else {
+	} else { /* indirect write */
+		/*
+		 * Have to lock the whole block to ensure when it's written out
+		 * and its checksum is being calculated that no one can change
+		 * the data. Contrarily to zfs_get_data we need not re-check
+		 * blocksize after we get the lock because it cannot be changed.
+		 */
 		size = zv->zv_volblocksize;
 		offset = P2ALIGN_TYPED(offset, size, uint64_t);
+		zgd->zgd_rl = zfs_range_lock(&zv->zv_range_lock, offset, size,
+		    RL_READER);
 		error = dmu_buf_hold_by_dnode(zv->zv_dn, offset, zgd, &db,
 		    DMU_READ_NO_PREFETCH);
 		if (error == 0) {

tests/runfiles/linux.run

@@ -594,7 +594,7 @@ tests = ['zvol_cli_001_pos', 'zvol_cli_002_pos', 'zvol_cli_003_neg']
 [tests/functional/zvol/zvol_misc]
 tests = ['zvol_misc_001_neg', 'zvol_misc_002_pos', 'zvol_misc_003_neg',
     'zvol_misc_004_pos', 'zvol_misc_005_neg', 'zvol_misc_006_pos',
-    'zvol_misc_snapdev', 'zvol_misc_volmode']
+    'zvol_misc_snapdev', 'zvol_misc_volmode', 'zvol_misc_zil']
 
 [tests/functional/zvol/zvol_swap]
 tests = ['zvol_swap_001_pos', 'zvol_swap_002_pos', 'zvol_swap_003_pos',

tests/zfs-tests/tests/functional/zvol/zvol_misc/Makefile.am

@@ -10,4 +10,5 @@ dist_pkgdata_SCRIPTS = \
 	zvol_misc_005_neg.ksh \
 	zvol_misc_006_pos.ksh \
 	zvol_misc_snapdev.ksh \
-	zvol_misc_volmode.ksh
+	zvol_misc_volmode.ksh \
+	zvol_misc_zil.ksh

tests/zfs-tests/tests/functional/zvol/zvol_misc/zvol_misc_zil.ksh

@@ -0,0 +1,74 @@
+#!/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 2017, loli10K <ezomori.nozomu@gmail.com>. All rights reserved.
+#
+
+. $STF_SUITE/include/libtest.shlib
+. $STF_SUITE/tests/functional/zvol/zvol_common.shlib
+. $STF_SUITE/tests/functional/zvol/zvol_misc/zvol_misc_common.kshlib
+
+#
+# DESCRIPTION:
+# Verify ZIL functionality on ZVOLs
+#
+# STRATEGY:
+# 1. Create a ZVOLs with various combination of "logbias" and "sync" values
+# 2. Write data to ZVOL device node
+# 3. Verify we don't trigger any issue like the one reported in #6238
+#
+
+verify_runnable "global"
+
+function cleanup
+{
+	datasetexists $ZVOL && log_must_busy zfs destroy $ZVOL
+	udev_wait
+}
+
+log_assert "Verify ZIL functionality on ZVOLs"
+log_onexit cleanup
+
+ZVOL="$TESTPOOL/vol"
+ZDEV="$ZVOL_DEVDIR/$ZVOL"
+typeset -a logbias_prop_vals=('latency' 'throughput')
+typeset -a sync_prop_vals=('standard' 'always' 'disabled')
+
+for logbias in ${logbias_prop_vals[@]}; do
+	for sync in ${sync_prop_vals[@]}; do
+		# 1. Create a ZVOL with logbias=throughput and sync=always
+		log_must zfs create -V $VOLSIZE -b 128K -o sync=$sync \
+		    -o logbias=$logbias $ZVOL
+
+		# 2. Write data to its device node
+		for i in {1..50}; do
+			dd if=/dev/zero of=$ZDEV bs=8k count=1 &
+		done
+
+		# 3. Verify we don't trigger any issue
+		log_must wait
+		log_must_busy zfs destroy $ZVOL
+	done
+done
+
+log_pass "ZIL functionality works on ZVOLs"