Without the barrier, reading DEAD flag of .q_usage_counter
and reading .mq_freeze_depth may be reordered, then the
following wait_event_interruptible() may never return.
Signed-off-by: Ming Lei <tom.leim...@gmail.com>
---
block/blk-core.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/block/blk-core.c b/block/blk-core.c
index ad388d5e309a..44eed17319c0 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -669,6 +669,14 @@ int blk_queue_enter(struct request_queue *q, bool nowait)
if (nowait)
return -EBUSY;
+ /*
+ * read pair of barrier in blk_mq_freeze_queue_start(),
+ * we need to order reading DEAD flag of .q_usage_counter
+ * and reading .mq_freeze_depth, otherwise the following
+ * wait may never return if the two read are reordered.
+ */
+ smp_rmb();
+
ret = wait_event_interruptible(q->mq_freeze_wq,
!atomic_read(&q->mq_freeze_depth) ||
blk_queue_dying(q));
--
2.9.3
