[PATCH 0/3 rfc] Fix nvme-tcp and nvme-rdma controller reset hangs

[Chao Leng]

On 2021/3/17 14:59, Christoph Hellwig wrote:
> On Wed, Mar 17, 2021 at 10:55:57AM +0800, Chao Leng wrote:
>>>> Will it work if nvme mpath used request NOWAIT flag for its submit_bio()
>>>> call, and add the bio to the requeue_list if blk_queue_enter() fails? I
>>>> think that looks like another way to resolve the deadlock, but we need
>>>> the block layer to return a failed status to the original caller.
> 
> Yes, I think BLK_MQ_REQ_NOWAIT makes total sense here.  dm-mpath also
> uses it for its request allocation for similar reasons.
> 
>>>
>>> But who would kick the requeue list? and that would make near-tag-exhaust performance stink...
> 
> The multipath code would have to kick the list.  We could also try to
> split into two flags, one that affects blk_queue_enter and one that
> affects the tag allocation.
> 
>> moving nvme_start_freeze from nvme_rdma_teardown_io_queues to nvme_rdma_configure_io_queues can fix it.
>> It can also avoid I/O hang long time if reconnection failed.
> 
> Can you explain how we'd still ensure that no new commands get queued
> during teardown using that scheme?
1. tear down will cancel all inflight requests, and then multipath will clear the path.
2. and then we may freeze the controler.
3. nvme_ns_head_submit_bio can not find the reconnection controller as valid path, so it is safe.
> .
>