blk-mq: don't use sync workqueue flushing from drivers

A previous commit introduced the sync flush, which we need from
internal callers like blk_mq_quiesce_queue(). However, we also
call the stop helpers from drivers, particularly from ->queue_rq()
when we have to stop processing for a bit. We can't block from
those locations, and we don't have to guarantee that we're
fully flushed.

Fixes: 9f993737 ("blk-mq: unify hctx delayed_run_work and run_work")
Reviewed-by: NBart Van Assche <Bart.VanAssche@sandisk.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

block/blk-mq.c

@@ -41,6 +41,7 @@ static LIST_HEAD(all_q_list);
 
 static void blk_mq_poll_stats_start(struct request_queue *q);
 static void blk_mq_poll_stats_fn(struct blk_stat_callback *cb);
+static void __blk_mq_stop_hw_queues(struct request_queue *q, bool sync);
 
 static int blk_mq_poll_stats_bkt(const struct request *rq)
 {
@@ -166,7 +167,7 @@ void blk_mq_quiesce_queue(struct request_queue *q)
 	unsigned int i;
 	bool rcu = false;
 
-	blk_mq_stop_hw_queues(q);
+	__blk_mq_stop_hw_queues(q, true);
 
 	queue_for_each_hw_ctx(q, hctx, i) {
 		if (hctx->flags & BLK_MQ_F_BLOCKING)
@@ -1218,20 +1219,34 @@ bool blk_mq_queue_stopped(struct request_queue *q)
 }
 EXPORT_SYMBOL(blk_mq_queue_stopped);
 
-void blk_mq_stop_hw_queue(struct blk_mq_hw_ctx *hctx)
+static void __blk_mq_stop_hw_queue(struct blk_mq_hw_ctx *hctx, bool sync)
 {
-	cancel_delayed_work_sync(&hctx->run_work);
+	if (sync)
+		cancel_delayed_work_sync(&hctx->run_work);
+	else
+		cancel_delayed_work(&hctx->run_work);
+
 	set_bit(BLK_MQ_S_STOPPED, &hctx->state);
 }
+
+void blk_mq_stop_hw_queue(struct blk_mq_hw_ctx *hctx)
+{
+	__blk_mq_stop_hw_queue(hctx, false);
+}
 EXPORT_SYMBOL(blk_mq_stop_hw_queue);
 
-void blk_mq_stop_hw_queues(struct request_queue *q)
+void __blk_mq_stop_hw_queues(struct request_queue *q, bool sync)
 {
 	struct blk_mq_hw_ctx *hctx;
 	int i;
 
 	queue_for_each_hw_ctx(q, hctx, i)
-		blk_mq_stop_hw_queue(hctx);
+		__blk_mq_stop_hw_queue(hctx, sync);
+}
+
+void blk_mq_stop_hw_queues(struct request_queue *q)
+{
+	__blk_mq_stop_hw_queues(q, false);
 }
 EXPORT_SYMBOL(blk_mq_stop_hw_queues);