dm: clear all discard attributes in queue_limits when discards are disabled

Otherwise, it can happen that the QUEUE_FLAG_DISCARD isn't set but the
various discard attributes (which get exposed via sysfs) may be set.
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm-table.c

@@ -1801,9 +1801,15 @@ void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
 	 */
 	q->limits = *limits;
 
-	if (!dm_table_supports_discards(t))
+	if (!dm_table_supports_discards(t)) {
 		queue_flag_clear_unlocked(QUEUE_FLAG_DISCARD, q);
-	else
+		/* Must also clear discard limits... */
+		q->limits.max_discard_sectors = 0;
+		q->limits.max_hw_discard_sectors = 0;
+		q->limits.discard_granularity = 0;
+		q->limits.discard_alignment = 0;
+		q->limits.discard_misaligned = 0;
+	} else
 		queue_flag_set_unlocked(QUEUE_FLAG_DISCARD, q);
 
 	if (dm_table_supports_flush(t, (1UL << QUEUE_FLAG_WC))) {