[PATCH 2/3] nvme-core: fix deadlock when reconnect failed due to nvme_set_queue_count timeout

[Christoph Hellwig]

On Thu, Aug 20, 2020 at 11:54:06AM +0800, Chao Leng wrote:
> A deadlock happens When we test nvme over roce with link blink. The
> reason: link blink will cause error recovery, and then reconnect.If
> reconnect fail due to nvme_set_queue_count timeout, the reconnect
> process will set the queue count as 0 and continue , and then
> nvme_start_ctrl will call nvme_enable_aen, and deadlock happens
> because the admin queue is quiesced.
> 
> log:
> Aug  3 22:47:24 localhost kernel: nvme nvme2: I/O 22 QID 0 timeout
> Aug  3 22:47:24 localhost kernel: nvme nvme2: Could not set queue count
> (881)
> stack:
> root     23848  0.0  0.0      0     0 ?        D    Aug03   0:00
> [kworker/u12:4+nvme-wq]
> [<0>] blk_execute_rq+0x69/0xa0
> [<0>] __nvme_submit_sync_cmd+0xaf/0x1b0 [nvme_core]
> [<0>] nvme_features+0x73/0xb0 [nvme_core]
> [<0>] nvme_start_ctrl+0xa4/0x100 [nvme_core]
> [<0>] nvme_rdma_setup_ctrl+0x438/0x700 [nvme_rdma]
> [<0>] nvme_rdma_reconnect_ctrl_work+0x22/0x30 [nvme_rdma]
> [<0>] process_one_work+0x1a7/0x370
> [<0>] worker_thread+0x30/0x380
> [<0>] kthread+0x112/0x130
> [<0>] ret_from_fork+0x35/0x40
> 
> Many functions which call __nvme_submit_sync_cmd treat error code in two
> modes: If error code less than 0, treat as command failed. If erroe code
> more than 0, treat as target not support or other and continue.
> NVME_SC_HOST_ABORTED_CMD and NVME_SC_HOST_PATH_ERROR both are cancled io
> by host, is not the real error code return from target. So we need set
> the flag:NVME_REQ_CANCELLED. Thus __nvme_submit_sync_cmd translate
> the error to INTR, nvme_set_queue_count will return error, reconnect
> process will terminate instead of continue.

But we could still race with a real completion.  I suspect the right
answer is to translate NVME_SC_HOST_ABORTED_CMD and
NVME_SC_HOST_PATH_ERROR to a negative error code in
__nvme_submit_sync_cmd.