[PATCHv2 2/2] nvme: Complete all stuck requests

[Sagi Grimberg]

>>> If the block layer has entered requests and gets a CPU hot plug event
>>> prior to the resume event, it will wait for those requests to exit. If
>>> the nvme driver is shutting down, it will not start the queues back up,
>>> preventing forward progress.
>>>
>>> To fix that, this patch freezes the request queues when the driver intends
>>> to shut down the controller so that no new requests may enter.  After the
>>> controller has been disabled, the queues will be restarted to force all
>>> entered requests to end in failure so that blk-mq's hot cpu notifier may
>>> progress. To ensure the queue usage count is 0 on a shutdown, the driver
>>> waits for freeze to complete before completing the controller shutdown.
>>
>> Keith, can you explain (again) for me why is the freeze_wait must happen
>> after the controller has been disabled, instead of starting the queues
>> and waiting right after freeze start?
>
> Yeah, the driver needs to make forward progress even if the controller
> isn't functioning. If we do the freeze wait before disabling the
> controller, there's no way to reclaim missing completions. If the
> controller is working perfectly, it'd be okay, but the driver would be
> stuck if there's a problem.

OK, I think we can get it for fabrics too, need to figure out how to
handle it there too.

Do you have a reproducer?