[PATCH v2 7/7] [RFC] nvme: Fix a race condition

[Bart Van Assche <bart.vanassche@sandisk.com>]

Avoid that nvme_queue_rq() is still running when nvme_stop_queues()
returns. Untested.

Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Cc: Keith Busch <keith.busch@intel.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Sagi Grimberg <sagi@grimberg.me>
---
 drivers/nvme/host/core.c | 20 ++++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index d791fba..98f1f29 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -201,13 +201,9 @@ fail:
 
 void nvme_requeue_req(struct request *req)
 {
-	unsigned long flags;
-
 	blk_mq_requeue_request(req);
-	spin_lock_irqsave(req->q->queue_lock, flags);
-	if (!blk_mq_queue_stopped(req->q))
-		blk_mq_kick_requeue_list(req->q);
-	spin_unlock_irqrestore(req->q->queue_lock, flags);
+	WARN_ON_ONCE(blk_mq_queue_stopped(req->q));
+	blk_mq_kick_requeue_list(req->q);
 }
 EXPORT_SYMBOL_GPL(nvme_requeue_req);
 
@@ -2077,11 +2073,19 @@ EXPORT_SYMBOL_GPL(nvme_kill_queues);
 void nvme_stop_queues(struct nvme_ctrl *ctrl)
 {
 	struct nvme_ns *ns;
+	struct request_queue *q;
 
 	mutex_lock(&ctrl->namespaces_mutex);
 	list_for_each_entry(ns, &ctrl->namespaces, list) {
-		blk_mq_cancel_requeue_work(ns->queue);
-		blk_mq_stop_hw_queues(ns->queue);
+		q = ns->queue;
+		blk_mq_quiesce_queue(q);
+		blk_mq_cancel_requeue_work(q);
+		blk_mq_stop_hw_queues(q);
+		/*
+		 * Note: blk_mq_resume_queue() does not affect the value
+		 * of the BLK_MQ_S_STOPPED bit.
+		 */
+		blk_mq_resume_queue(q);
 	}
 	mutex_unlock(&ctrl->namespaces_mutex);
 }
-- 
2.10.0