Re: [PATCH v3 2/4] block: add a read barrier in blk_queue_enter()
From: Bart Van Assche <hidden>
Date: 2017-03-27 15:44:10
On Mon, 2017-03-27 at 20:06 +0800, Ming Lei wrote:
quoted hunk ↗ jump to hunk
diff --git a/block/blk-core.c b/block/blk-core.c index ad388d5e309a..5e8963bc98d9 100644 --- a/block/blk-core.c +++ b/block/blk-core.c@@ -669,6 +669,15 @@ int blk_queue_enter(struct request_queue *q, bool no=
wait)
if (nowait) return -EBUSY; =20 + /* + * read pair of barrier in blk_mq_freeze_queue_start(), + * we need to order reading __PERCPU_REF_DEAD flag of + * .q_usage_counter and reading .mq_freeze_depth, + * otherwise the following wait may never return if the + * two reads are reordered. + */ + smp_rmb(); + ret =3D wait_event_interruptible(q->mq_freeze_wq, !atomic_read(&q->mq_freeze_depth) || blk_queue_dying(q));
Since patch 4/4 modifies the comment introduced by this patch, I would have preferred that patches 2/4 and 4/4 would have been combined into a single patch. Anyway: Reviewed-by: Bart Van Assche <redacted>