Re: [PATCH 1/2] nvme: pci: simplify timeout handling

[Ming Lei <ming.lei@redhat.com>]

On Fri, Apr 27, 2018 at 09:37:06AM +0800, jianchao.wang wrote:
> 
> 
> On 04/26/2018 11:57 PM, Ming Lei wrote:
> > Hi Jianchao,
> > 
> > On Thu, Apr 26, 2018 at 11:07:56PM +0800, jianchao.wang wrote:
> >> Hi Ming
> >>
> >> Thanks for your wonderful solution. :)
> >>
> >> On 04/26/2018 08:39 PM, Ming Lei wrote:
> >>> +/*
> >>> + * This one is called after queues are quiesced, and no in-fligh timeout
> >>> + * and nvme interrupt handling.
> >>> + */
> >>> +static void nvme_pci_cancel_request(struct request *req, void *data,
> >>> +		bool reserved)
> >>> +{
> >>> +	/* make sure timed-out requests are covered too */
> >>> +	if (req->rq_flags & RQF_MQ_TIMEOUT_EXPIRED) {
> >>> +		req->aborted_gstate = 0;
> >>> +		req->rq_flags &= ~RQF_MQ_TIMEOUT_EXPIRED;
> >>> +	}
> >>> +
> >>> +	nvme_cancel_request(req, data, reserved);
> >>> +}
> >>> +
> >>>  static void nvme_dev_disable(struct nvme_dev *dev, bool shutdown)
> >>>  {
> >>>  	int i;
> >>> @@ -2223,10 +2316,17 @@ static void nvme_dev_disable(struct nvme_dev *dev, bool shutdown)
> >>>  	for (i = dev->ctrl.queue_count - 1; i >= 0; i--)
> >>>  		nvme_suspend_queue(&dev->queues[i]);
> >>>  
> >>> +	/*
> >>> +	 * safe to sync timeout after queues are quiesced, then all
> >>> +	 * requests(include the time-out ones) will be canceled.
> >>> +	 */
> >>> +	nvme_sync_queues(&dev->ctrl);
> >>> +	blk_sync_queue(dev->ctrl.admin_q);
> >>> +
> >> Looks like blk_sync_queue cannot drain all the timeout work.
> >>
> >> blk_sync_queue
> >>   -> del_timer_sync          
> >>                           blk_mq_timeout_work
> >>                             -> mod_timer
> >>   -> cancel_work_sync
> >> the timeout work may come back again.
> >> we may need to force all the in-flight requests to be timed out with blk_abort_request
> >>
> > 
> > blk_abort_request() seems over-kill, we could avoid this race simply by
> > returning EH_NOT_HANDLED if the controller is in-recovery.
> return EH_NOT_HANDLED maybe not enough.
> please consider the following scenario.
> 
>                                       nvme_error_handler
>                                         -> nvme_dev_disable
>                                           -> blk_sync_queue
> //timeout comes again due to the
> //scenario above

I may not understand your point, once blk_sync_queue() returns, the
timer itself is deactivated, meantime the synced .nvme_timeout() only
returns EH_NOT_HANDLED before the deactivation.

That means this timer won't be expired any more, so could you explain
a bit why timeout can come again after blk_sync_queue() returns.

Thanks,
Ming