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Date:   Thu, 18 Jan 2018 23:05:21 -0700
From:   Keith Busch <keith.busch@intel.com>
To:     "jianchao.wang" <jianchao.w.wang@oracle.com>
Cc:     axboe@fb.com, hch@lst.de, sagi@grimberg.me, maxg@mellanox.com,
        james.smart@broadcom.com, linux-nvme@lists.infradead.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH V5 2/2] nvme-pci: fixup the timeout case when reset is
 ongoing
Message-ID: <20180119060521.GD12043@localhost.localdomain>
References: <1516270202-8051-1-git-send-email-jianchao.w.wang@oracle.com>
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On Fri, Jan 19, 2018 at 01:55:29PM +0800, jianchao.wang wrote:
> On 01/19/2018 12:59 PM, Keith Busch wrote:
> > On Thu, Jan 18, 2018 at 06:10:02PM +0800, Jianchao Wang wrote:
> >> +	 * - When the ctrl.state is NVME_CTRL_RESETTING, the expired
> >> +	 *   request should come from the previous work and we handle
> >> +	 *   it as nvme_cancel_request.
> >> +	 * - When the ctrl.state is NVME_CTRL_RECONNECTING, the expired
> >> +	 *   request should come from the initializing procedure such as
> >> +	 *   setup io queues, because all the previous outstanding
> >> +	 *   requests should have been cancelled.
> >>  	 */
> >> -	if (dev->ctrl.state == NVME_CTRL_RESETTING) {
> >> -		dev_warn(dev->ctrl.device,
> >> -			 "I/O %d QID %d timeout, disable controller\n",
> >> -			 req->tag, nvmeq->qid);
> >> -		nvme_dev_disable(dev, false);
> >> +	switch (dev->ctrl.state) {
> >> +	case NVME_CTRL_RESETTING:
> >> +		nvme_req(req)->status = NVME_SC_ABORT_REQ;
> >> +		return BLK_EH_HANDLED;
> >> +	case NVME_CTRL_RECONNECTING:
> >> +		WARN_ON_ONCE(nvmeq->qid);
> >>  		nvme_req(req)->flags |= NVME_REQ_CANCELLED;
> >>  		return BLK_EH_HANDLED;
> >> +	default:
> >> +		break;
> >>  	}
> > 
> > The driver may be giving up on the command here, but that doesn't mean
> > the controller has. We can't just end the request like this because that
> > will release the memory the controller still owns. We must wait until
> > after nvme_dev_disable clears bus master because we can't say for sure
> > the controller isn't going to write to that address right after we end
> > the request.
> > 
> Yes, but the controller is going to be reseted or shutdown at the moment,
> even if the controller accesses a bad address and goes wrong, everything will
> be ok after reset or shutdown. :)

Hm, I don't follow. DMA access after free is never okay.