Re: [RFC PATCH 2/5] block: Do not stop draining if waitqueue is not empty.

[Tejun Heo <tj@kernel.org>]

Hello, Asias.

On Tue, May 22, 2012 at 02:48:55PM +0800, Asias He wrote:
> I actually saw this happened though it should not happen. I have no
> idea why this happens. Maybe unbalanced prepare_to_wait_exclusive()
> in get_request_wait() and wake_up() in __freed_request()?

Hmm.... unbalanced how?  I think bugs in this area are much more
likely to show up as live queue hang rather than issues during queue
shutdown.

> With this happened, I saw some fio threads in D state which are
> sleeping on get_request_wait(). If I wake up the threads in the wait
> queue in q->abort_queue_fn() callback which i proposed in the 1/5 of
> this patch set, the queue cleanup and thus hot-unplug went pretty
> well. (Passed 3000~ rounds of test, without this 2~ round of test
> would fail). See this patch [RFC PATCH 4/5] virtio-blk: Use
> q->abort_queue_fn() to abort.

If the problem is that easily reproducible (you mean that you can
reproduce it every other time, right?), it would be immensely helpful
if you can root cause the issue properly.  As it currently stands,
this series seems to work around the problem by adding extra API
without properly root-causing it.  Workarounds without proper
root-causing are already pretty bad and adding extra API for that is
rather silly, IMHO.

Thanks.

-- 
tejun