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

[Keith Busch <keith.busch@linux.intel.com>]

On Fri, May 11, 2018 at 04:52:11AM +0800, Ming Lei wrote:
> Hi Keith,
> 
> On Tue, May 8, 2018 at 11:30 PM, Keith Busch <keith.busch@intel.com> wrote:
> > On Sat, Apr 28, 2018 at 11:50:17AM +0800, Ming Lei wrote:
> >> This sync may be raced with one timed-out request, which may be handled
> >> as BLK_EH_HANDLED or BLK_EH_RESET_TIMER, so the above sync queues can't
> >> work reliably.
> >
> > Ming,
> >
> > As proposed, that scenario is impossible to encounter. Resetting the
> > controller inline with the timeout reaps all the commands, and then
> > sets the controller state to RESETTING. While blk-mq may not allow the
> > driver to complete those requests, having the driver sync with the queues
> > will hold the controller in the reset state until blk-mq is done with
> > its timeout work; therefore, it is impossible for the NVMe driver to
> > return "BLK_EH_RESET_TIMER", and all commands will be completed through
> > nvme_timeout's BLK_EH_HANDLED exactly as desired.
> 
> That isn't true for multiple namespace case,  each request queue has its
> own timeout work, and all these timeout work can be triggered concurrently.

The controller state is most certainly not per queue/namespace. It's
global to the controller. Once the reset is triggered, nvme_timeout can
only return EH_HANDLED.