From: Sagi Grimberg sagi@grimberg.me
[ Upstream commit 3770a42bb8ceb856877699257a43c0585a5d2996 ]
When we queue requests, we strive to batch as much as possible and also signal the network stack that more data is about to be sent over a socket with MSG_SENDPAGE_NOTLAST. This flag looks at the pending requests queued as well as queue->more_requests that is derived from the block layer last-in-batch indication.
We set more_request=true when we flush the request directly from .queue_rq submission context (in nvme_tcp_send_all), however this is wrongly assuming that no other requests may be queued during the execution of nvme_tcp_send_all.
Due to this, a race condition may happen where:
1. request X is queued as !last-in-batch 2. request X submission context calls nvme_tcp_send_all directly 3. nvme_tcp_send_all is preempted and schedules to a different cpu 4. request Y is queued as last-in-batch 5. nvme_tcp_send_all context sends request X+Y, however signals for both MSG_SENDPAGE_NOTLAST because queue->more_requests=true.
==> none of the requests is pushed down to the wire as the network stack is waiting for more data, both requests timeout.
To fix this, we eliminate queue->more_requests and only rely on the queue req_list and send_list to be not-empty.
Fixes: 122e5b9f3d37 ("nvme-tcp: optimize network stack with setting msg flags according to batch size") Reported-by: Jonathan Nicklin jnicklin@blockbridge.com Signed-off-by: Sagi Grimberg sagi@grimberg.me Tested-by: Jonathan Nicklin jnicklin@blockbridge.com Signed-off-by: Christoph Hellwig hch@lst.de Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/nvme/host/tcp.c | 5 +---- 1 file changed, 1 insertion(+), 4 deletions(-)
diff --git a/drivers/nvme/host/tcp.c b/drivers/nvme/host/tcp.c index 2c6e031135716..96d8d7844e846 100644 --- a/drivers/nvme/host/tcp.c +++ b/drivers/nvme/host/tcp.c @@ -119,7 +119,6 @@ struct nvme_tcp_queue { struct mutex send_mutex; struct llist_head req_list; struct list_head send_list; - bool more_requests;
/* recv state */ void *pdu; @@ -315,7 +314,7 @@ static inline void nvme_tcp_send_all(struct nvme_tcp_queue *queue) static inline bool nvme_tcp_queue_more(struct nvme_tcp_queue *queue) { return !list_empty(&queue->send_list) || - !llist_empty(&queue->req_list) || queue->more_requests; + !llist_empty(&queue->req_list); }
static inline void nvme_tcp_queue_request(struct nvme_tcp_request *req, @@ -334,9 +333,7 @@ static inline void nvme_tcp_queue_request(struct nvme_tcp_request *req, */ if (queue->io_cpu == raw_smp_processor_id() && sync && empty && mutex_trylock(&queue->send_mutex)) { - queue->more_requests = !last; nvme_tcp_send_all(queue); - queue->more_requests = false; mutex_unlock(&queue->send_mutex); }