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

[Keith Busch]

On Thu, Mar 18, 2021 at 11:46:08AM -0700, Sagi Grimberg wrote:
> 
> Placing the request on the requeue_list is fine, but the question is
> when to kick the requeue_work, nothing guarantees that an alternate path
> exist or will in a sane period. So constantly requeue+kick sounds like
> a really bad practice to me.

nvme_mpath_set_live(), where you reported the deadlock, kicks the
requeue_list. The difference that NOWAIT provides is that
nvme_mpath_set_live's schronize_srcu() is no longer blocked forever
because the .submit_bio() isn't waiting for entery on a frozen queue, so
now it's free to schedule the dispatch.

There's probably an optimization to kick it sooner if there's a viable
alternate path, but that could be a follow on.

If there's no immediate viable path, then the requests would remain on
the requeue list. That currently happens as long as there's a potential
controller in a reset or connecting state.