Re: [PATCH 5/5] nvme: use __blk_mq_complete_request in timeout path

[Sagi Grimberg]

> Hi Christoph
>
> Thanks for your kindly response.
>
> On 06/20/2018 10:39 PM, Christoph Hellwig wrote:
> > > diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
> > > index 73a97fc..2a161f6 100644
> > > --- a/drivers/nvme/host/pci.c
> > > +++ b/drivers/nvme/host/pci.c
> > > @@ -1203,6 +1203,7 @@ static enum blk_eh_timer_return nvme_timeout(struct request *req, bool reserved)
> > >   		nvme_warn_reset(dev, csts);
> > >   		nvme_dev_disable(dev, false);
> > >   		nvme_reset_ctrl(&dev->ctrl);
> > > +		__blk_mq_complete_request(req);
> > >   		return BLK_EH_DONE;
> > >   	}
> > >   
> > > @@ -1213,6 +1214,11 @@ static enum blk_eh_timer_return nvme_timeout(struct request *req, bool reserved)
> > >   		dev_warn(dev->ctrl.device,
> > >   			 "I/O %d QID %d timeout, completion polled\n",
> > >   			 req->tag, nvmeq->qid);
> > > +		/*
> > > +		 * nvme_end_request will invoke blk_mq_complete_request,
> > > +		 * it will do nothing for this timed out request.
> > > +		 */
> > > +		__blk_mq_complete_request(req);
> >
> > And this clearly is bogus.  We want to iterate over the tagetset
> > and cancel all requests, not do that manually here.
> >
> > That was the whole point of the original change.
>
> For nvme-pci, we indeed have an issue that when nvme_reset_work->nvme_dev_disable returns, timeout path maybe still
> running and the nvme_dev_disable invoked by timeout path will race with the nvme_reset_work.
> However, the hole is still there right now w/o my changes, but just narrower.

Given the amount of fixes (and fixes of fixes) we had in the timeout 
handler, maybe it'd be a good idea to step back and take a another look?

Won't it be better to avoid disabling the device and return
BLK_EH_RESET_TIMER if we are not aborting in the timeout handler?