On Fri, May 11, 2018 at 5:18 AM, Keith Busch <keith.busch@xxxxxxxxxxxxxxx> 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. Sorry, forget to mention, it isn't enough to simply sync timeout inside reset(). Another tricky thing is about freeze & unfreeze, now freeze is done in nvme_dev_disable(), and unfreeze is done in nvme_reset_work. That means we have to make sure both are paired, otherwise queues may be kept as freeze for ever. This issue is covered by my V4 & V5 too. thanks, Ming Lei
