blk-mq: Let drivers cancel requeue_work

Kicking requeued requests will start h/w queues in a work_queue, which
may alter the driver's requested state to temporarily stop them. This
patch exports a method to cancel the q->requeue_work so a driver can be
assured stopped h/w queues won't be started up before it is ready.
Signed-off-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

block/blk-mq.c

@@ -527,6 +527,12 @@ void blk_mq_add_to_requeue_list(struct request *rq, bool at_head)
 }
 EXPORT_SYMBOL(blk_mq_add_to_requeue_list);
 
+void blk_mq_cancel_requeue_work(struct request_queue *q)
+{
+	cancel_work_sync(&q->requeue_work);
+}
+EXPORT_SYMBOL_GPL(blk_mq_cancel_requeue_work);
+
 void blk_mq_kick_requeue_list(struct request_queue *q)
 {
 	kblockd_schedule_work(&q->requeue_work);

include/linux/blk-mq.h

@@ -201,6 +201,7 @@ void __blk_mq_end_request(struct request *rq, int error);
 
 void blk_mq_requeue_request(struct request *rq);
 void blk_mq_add_to_requeue_list(struct request *rq, bool at_head);
+void blk_mq_cancel_requeue_work(struct request_queue *q);
 void blk_mq_kick_requeue_list(struct request_queue *q);
 void blk_mq_complete_request(struct request *rq);