[PATCH AUTOSEL 5.13 17/26] blk-mq: don't grab rq's refcount in blk_mq_check_expired()

Sasha Levin
2021-08-24T00:55:30Z

From: Ming Lei <ming.lei@redhat.com>

[ Upstream commit c797b40ccc340b8a66f7a7842aecc90bf749f087 ]

Inside blk_mq_queue_tag_busy_iter() we already grabbed request's
refcount before calling ->fn(), so needn't to grab it one more time
in blk_mq_check_expired().

Meantime remove extra request expire check in blk_mq_check_expired().

Cc: Keith Busch <kbusch@kernel.org>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: John Garry <john.garry@huawei.com>
Link: https://lore.kernel.org/r/20210811155202.629575-1-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
block/blk-mq.c | 30 +++++-------------------------
1 file changed, 5 insertions(+), 25 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index c732aa581124..6dfa572ac1fc 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -923,34 +923,14 @@ static bool blk_mq_check_expired(struct blk_mq_hw_ctx *hctx,
unsigned long *next = priv;

/*
- * Just do a quick check if it is expired before locking the request in
- * so we're not unnecessarilly synchronizing across CPUs.
- */
- if (!blk_mq_req_expired(rq, next))
- return true;
-
- /*
- * We have reason to believe the request may be expired. Take a
- * reference on the request to lock this request lifetime into its
- * currently allocated context to prevent it from being reallocated in
- * the event the completion by-passes this timeout handler.
- *
- * If the reference was already released, then the driver beat the
- * timeout handler to posting a natural completion.
- */
- if (!refcount_inc_not_zero(&rq->ref))
- return true;
-
- /*
- * The request is now locked and cannot be reallocated underneath the
- * timeout handler's processing. Re-verify this exact request is truly
- * expired; if it is not expired, then the request was completed and
- * reallocated as a new request.
+ * blk_mq_queue_tag_busy_iter() has locked the request, so it cannot
+ * be reallocated underneath the timeout handler's processing, then
+ * the expire check is reliable. If the request is not expired, then
+ * it was completed and reallocated as a new request after returning
+ * from blk_mq_check_expired().
*/
if (blk_mq_req_expired(rq, next))
blk_mq_rq_timed_out(rq, reserved);
-
- blk_mq_put_rq_ref(rq);
return true;
}

--
2.30.2