lockdep WARNING at blktests block/011

[Keith Busch]

On Fri, Oct 7, 2022 at 10:34 PM Bart Van Assche <bvanassche at acm.org> wrote:
>
> On 10/3/22 08:28, Keith Busch wrote:
> > On Mon, Oct 03, 2022 at 01:32:41PM +0000, Shinichiro Kawasaki wrote:
> >>
> >> BTW, I came up to another question during code read. I found nvme_reset_work()
> >> calls nvme_dev_disable() before nvme_sync_queues(). So, I think the NVME
> >> controller is already disabled when the reset work calls nvme_sync_queues().
> >
> > Right, everything previously outstanding has been reclaimed, and the queues are
> > quiesced at this point. There's nothing for timeout work to wait for, and the
> > sync is just ensuring every timeout work has returned.
> >
> > It looks like a timeout is required in order to hit this reported deadlock, but
> > the driver ensures there's nothing to timeout prior to syncing the queues. I
> > don't think lockdep could reasonably know that, though.
>
> Hi Keith,
>
> Commit b2a0eb1a0ac7 ("nvme-pci: Remove watchdog timer") introduced the
> nvme_dev_disable() and nvme_reset_ctrl() calls in the nvme_timeout()
> function. Has it been considered to invoke these two calls asynchronously
> instead of synchronously from the NVMe timeout handler (queue_work())?
> Although it may require some work to make sure that this approach does not
> trigger any race conditions, do you agree that this should be sufficient to
> make lockdep happy?

We still have to sync whatever work does the reset, so that would just
shift which work the lockdep splat indicates.