On Thu, May 10, 2018 at 03:18:29PM -0600, Keith Busch wrote: > On Fri, May 11, 2018 at 05:10:40AM +0800, Ming Lei wrote: > > On Fri, May 11, 2018 at 5:05 AM, Keith Busch > > <keith.busch@xxxxxxxxxxxxxxx> wrote: > > > 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@xxxxxxxxx> 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. > > > > It is related with EH_HANDLED, please see the following case: > > > > 1) when req A from N1 is timed out, nvme_timeout() handles > > it as EH_HANDLED: nvme_dev_disable() and reset is scheduled. > > > > 2) when req B from N2 is timed out, nvme_timeout() handles > > it as EH_HANDLED, then nvme_dev_disable() is called exactly > > when reset is in-progress, so queues become quiesced, and nothing > > can move on in the resetting triggered by N1. > > Huh? The nvme_sync_queues ensures that doesn't happen. That was the > whole point. Could you share me the link? Firstly, the previous nvme_sync_queues() won't work reliably, so this patch introduces blk_unquiesce_timeout() and blk_quiesce_timeout() for this purpose. Secondly, I remembered that you only call nvme_sync_queues() at the entry of nvme_reset_work(), but timeout(either admin or normal IO) can happen again during resetting, that is another race addressed by this patchset, but can't cover by your proposal. Thanks, Ming
