On Wed, Mar 17, 2021 at 10:55:57AM +0800, Chao Leng wrote:

quoted

quoted

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.

quoted

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?

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