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-rw-r--r--block/blk-barrier.c14
1 files changed, 13 insertions, 1 deletions
diff --git a/block/blk-barrier.c b/block/blk-barrier.c
index c63044e9c4c..8eba4e43bb0 100644
--- a/block/blk-barrier.c
+++ b/block/blk-barrier.c
@@ -166,9 +166,21 @@ static inline bool start_ordered(struct request_queue *q, struct request **rqp)
* For an empty barrier, there's no actual BAR request, which
* in turn makes POSTFLUSH unnecessary. Mask them off.
*/
- if (!rq->hard_nr_sectors)
+ if (!rq->hard_nr_sectors) {
q->ordered &= ~(QUEUE_ORDERED_DO_BAR |
QUEUE_ORDERED_DO_POSTFLUSH);
+ /*
+ * Empty barrier on a write-through device w/ ordered
+ * tag has no command to issue and without any command
+ * to issue, ordering by tag can't be used. Drain
+ * instead.
+ */
+ if ((q->ordered & QUEUE_ORDERED_BY_TAG) &&
+ !(q->ordered & QUEUE_ORDERED_DO_PREFLUSH)) {
+ q->ordered &= ~QUEUE_ORDERED_BY_TAG;
+ q->ordered |= QUEUE_ORDERED_BY_DRAIN;
+ }
+ }
/* stash away the original request */
elv_dequeue_request(q, rq);