This is a note to let you know that I've just added the patch titled
nvme-tcp: fix io_work priority inversion
to the 5.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
nvme-tcp-fix-io_work-priority-inversion.patch
and it can be found in the queue-5.14 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit cf44fd56a5dbf25702cafd2470d67626c4a19aa3
Author: Keith Busch <kbusch@xxxxxxxxxx>
Date: Thu Sep 9 08:54:52 2021 -0700
nvme-tcp: fix io_work priority inversion
[ Upstream commit 70f437fb4395ad4d1d16fab9a1ad9fbc9fc0579b ]
Dispatching requests inline with the .queue_rq() call may block while
holding the send_mutex. If the tcp io_work also happens to schedule, it
may see the req_list is non-empty, leaving "pending" true and remaining
in TASK_RUNNING. Since io_work is of higher scheduling priority, the
.queue_rq task may not get a chance to run, blocking forward progress
and leading to io timeouts.
Instead of checking for pending requests within io_work, let the queueing
restart io_work outside the send_mutex lock if there is more work to be
done.
Fixes: a0fdd1418007f ("nvme-tcp: rerun io_work if req_list is not empty")
Reported-by: Samuel Jones <sjones@xxxxxxxxxxxxx>
Signed-off-by: Keith Busch <kbusch@xxxxxxxxxx>
Reviewed-by: Sagi Grimberg <sagi@xxxxxxxxxxx>
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/drivers/nvme/host/tcp.c b/drivers/nvme/host/tcp.c
index 48b70e5235a3..19a711395cdc 100644
--- a/drivers/nvme/host/tcp.c
+++ b/drivers/nvme/host/tcp.c
@@ -273,6 +273,12 @@ static inline void nvme_tcp_send_all(struct nvme_tcp_queue *queue)
} while (ret > 0);
}
+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;
+}
+
static inline void nvme_tcp_queue_request(struct nvme_tcp_request *req,
bool sync, bool last)
{
@@ -293,9 +299,10 @@ static inline void nvme_tcp_queue_request(struct nvme_tcp_request *req,
nvme_tcp_send_all(queue);
queue->more_requests = false;
mutex_unlock(&queue->send_mutex);
- } else if (last) {
- queue_work_on(queue->io_cpu, nvme_tcp_wq, &queue->io_work);
}
+
+ if (last && nvme_tcp_queue_more(queue))
+ queue_work_on(queue->io_cpu, nvme_tcp_wq, &queue->io_work);
}
static void nvme_tcp_process_req_list(struct nvme_tcp_queue *queue)
@@ -893,12 +900,6 @@ done:
read_unlock_bh(&sk->sk_callback_lock);
}
-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;
-}
-
static inline void nvme_tcp_done_send_req(struct nvme_tcp_queue *queue)
{
queue->request = NULL;
@@ -1132,8 +1133,7 @@ static void nvme_tcp_io_work(struct work_struct *w)
pending = true;
else if (unlikely(result < 0))
break;
- } else
- pending = !llist_empty(&queue->req_list);
+ }
result = nvme_tcp_try_recv(queue);
if (result > 0)
