[PATCH 2/6] nvme-pci: Don't disable on timeout in reset state

[kbusch@kernel.org (Keith Busch)]

On Wed, May 15, 2019@08:07:09PM -0700, Ming Lei wrote:
> On Wed, May 15, 2019@10:36:21AM -0600, Keith Busch wrote:
> > The driver doesn't dispatch commands that it needs to wait for in the reset
> > state anymore. If a timeout occurs in this state, the reset work is
> > already disabling the controller, so just reset the request's timer.
> > 
> > Signed-off-by: Keith Busch <keith.busch at intel.com>
> > ---
> >  drivers/nvme/host/pci.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
> > index d4e442160048..c72755311ffa 100644
> > --- a/drivers/nvme/host/pci.c
> > +++ b/drivers/nvme/host/pci.c
> > @@ -1298,13 +1298,14 @@ static enum blk_eh_timer_return nvme_timeout(struct request *req, bool reserved)
> >  		shutdown = true;
> >  		/* fall through */
> >  	case NVME_CTRL_CONNECTING:
> > -	case NVME_CTRL_RESETTING:
> >  		dev_warn_ratelimited(dev->ctrl.device,
> >  			 "I/O %d QID %d timeout, disable controller\n",
> >  			 req->tag, nvmeq->qid);
> >  		nvme_dev_disable(dev, shutdown);
> >  		nvme_req(req)->flags |= NVME_REQ_CANCELLED;
> >  		return BLK_EH_DONE;
> > +	case NVME_CTRL_RESETTING:
> > +		return BLK_EH_RESET_TIMER;
> >  	default:
> >  		break;
> >  	}
> 
> RESET follows controller shutdown(via nvme_dev_disable()), the only
> possible timeout should be on admin requests staggered between shutdown
> and changing to NVME_CTRL_CONNECTING, given admin queue isn't frozen.
> 
> And the admin queue should be fully workable after it is unquiesced
> by nvme_alloc_admin_tags(), so if timeout happens after nvme_alloc_admin_tags(),
> I guess these requests should be handled as in NVME_CTRL_CONNECTING.

Yep, the only timeouts here should be requests that we've already
reclaimed, or are about to reclaim, via nvme_dev_disable called
from either another timeout work or directly in the reset_work. And
nvme_dev_disable handles its timeout, so we don't need timeout work to
unblock it. Either way, we're never blocked in the RESETTING state.

> Another related problem is about handling timeout in NVME_CTRL_CONNECTING, and
> the following failure still can be observed:
> 
> [ 1078.775969] nvme nvme0: I/O 20 QID 0 timeout, disable controller
> [ 1078.791730] nvme nvme0: Identify Controller failed (-4)
> [ 1078.792538] nvme nvme0: Removing after probe failure status: -5

Right, we will fail the controller if it fails to produce a response to
any initialization commands. It's either that, or try the same thing
atateain, but I haven't seen much support for doing the latter.