blk-mq: don't grab rq's refcount in blk_mq_check_expired()

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>

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 2fe3963..914c71e 100644 (file)
--- 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;
 }