dm: lock limits when reading them

Lock queue limits when reading them, so that we don't read halfway
modified values.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Cc: stable@vger.kernel.org

Author: Mikulas Patocka

drivers/md/dm-table.c

@@ -431,6 +431,7 @@ static int dm_set_device_limits(struct dm_target *ti, struct dm_dev *dev,
 		return 0;
 	}
 
+	mutex_lock(&q->limits_lock);
 	if (blk_stack_limits(limits, &q->limits,
 			get_start_sect(bdev) + start) < 0)
 		DMWARN("%s: adding target device %pg caused an alignment inconsistency: "
@@ -448,6 +449,7 @@ static int dm_set_device_limits(struct dm_target *ti, struct dm_dev *dev,
 	 */
 	if (!dm_target_has_integrity(ti->type))
 		queue_limits_stack_integrity_bdev(limits, bdev);
+	mutex_unlock(&q->limits_lock);
 	return 0;
 }
 
@@ -1734,8 +1736,12 @@ static int device_not_write_zeroes_capable(struct dm_target *ti, struct dm_dev *
 					   sector_t start, sector_t len, void *data)
 {
 	struct request_queue *q = bdev_get_queue(dev->bdev);
+	int b;
 
-	return !q->limits.max_write_zeroes_sectors;
+	mutex_lock(&q->limits_lock);
+	b = !q->limits.max_write_zeroes_sectors;
+	mutex_unlock(&q->limits_lock);
+	return b;
 }
 
 static bool dm_table_supports_write_zeroes(struct dm_table *t)