[PATCHv3 3/3] blk-mq: Simplify request completion state

[Keith Busch <keith.busch@intel.com>]

There are no more users relying on blk-mq request states to prevent
double completions, so replace the relatively expensive cmpxchg operation
with WRITE_ONCE.

Signed-off-by: Keith Busch <keith.busch@intel.com>
---
 block/blk-mq.c         |  4 +---
 include/linux/blk-mq.h | 14 --------------
 2 files changed, 1 insertion(+), 17 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 1fb0f2050d31..ce769132cfbe 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -568,9 +568,7 @@ static void __blk_mq_complete_request(struct request *rq)
 	bool shared = false;
 	int cpu;
 
-	if (!blk_mq_mark_complete(rq))
-		return;
-
+	WRITE_ONCE(rq->state, MQ_RQ_COMPLETE);
 	/*
 	 * Most of single queue controllers, there is only one irq vector
 	 * for handling IO completion, and the only irq's affinity is set
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index f0dc26fc86a9..9b5528fcdd45 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -329,20 +329,6 @@ void blk_mq_quiesce_queue_nowait(struct request_queue *q);
 
 unsigned int blk_mq_rq_cpu(struct request *rq);
 
-/**
- * blk_mq_mark_complete() - Set request state to complete
- * @rq: request to set to complete state
- *
- * Returns true if request state was successfully set to complete. If
- * successful, the caller is responsibile for seeing this request is ended, as
- * blk_mq_complete_request will not work again.
- */
-static inline bool blk_mq_mark_complete(struct request *rq)
-{
-	return cmpxchg(&rq->state, MQ_RQ_IN_FLIGHT, MQ_RQ_COMPLETE) ==
-			MQ_RQ_IN_FLIGHT;
-}
-
 /*
  * Driver command data is immediately after the request. So subtract request
  * size to get back to the original request, add request size to get the PDU.
-- 
2.14.4