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nvme-tcp: fix io_work priority inversion 

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: a0fdd14180 ("nvme-tcp: rerun io_work if req_list is not empty")
Reported-by: Samuel Jones <sjones@kalrayinc.com>
Signed-off-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Christoph Hellwig <hch@lst.de>
This commit is contained in:
Keith Busch 2021-09-09 08:54:52 -07:00 committed by Christoph Hellwig
parent 9817d763db
commit 70f437fb43
1 changed files with 10 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

20
drivers/nvme/host/tcp.c
View File

@ -274,6 +274,12 @@ 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)
{
@ -294,9 +300,10 @@ 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)
@ -906,12 +913,6 @@ static void nvme_tcp_state_change(struct sock *sk)
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;
@ -1145,8 +1146,7 @@ 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)