Re: [Patch v4 10/10] i2x: pnx: Use threaded irq to fix warning from del_timer_sync()

Piotr Wojtaszczyk
2024-06-27T11:06:05Z

On Tue, Jun 25, 2024 at 11:12 PM Andi Shyti <andi.shyti@kernel.org> wrote:
>
> Hi Piotr,
>
> On Fri, Jun 21, 2024 at 02:08:03PM GMT, Piotr Wojtaszczyk wrote:
> > On Fri, Jun 21, 2024 at 12:57 AM Andi Shyti <andi.shyti@kernel.org> wrote:
> > > On Thu, Jun 20, 2024 at 07:56:41PM GMT, Piotr Wojtaszczyk wrote:
> > > > When del_timer_sync() is called in an interrupt context it throws a warning
> > > > because of potential deadlock. Threaded irq handler fixes the potential
> > > > problem.
> > > >
> > > > Signed-off-by: Piotr Wojtaszczyk <piotr.wojtaszczyk@timesys.com>
> > >
> > > did you run into a lockdep splat?
> > >
> > > Anything against using del_timer(), instead? Have you tried?
> >
> > I didn't get a lockdep splat but console was flooded with warnings from
> > https://github.com/torvalds/linux/blob/v6.10-rc4/kernel/time/timer.c#L1655
> > In the linux kernel v5.15 I didn't see these warnings.
> >
> > I'm not a maintainer of the driver and I didn't do any research on
> > what kind of impact
> > would have using del_timer() instad. Maybe Vladimir Zapolskiy will know that.
>
> Your patch is definitely correct, no doubt about that.
>
> And I don't have anything aginast changing irq handlers to
> threaded handlers. But I would be careful at doing that depending
> on the use of the controller and for accepting such change I
> would need an ack from someone who knows the device. Vladimir,
> perhaps?
>
> There are cases where using threaded handlers are not totally
> right, for example when the controller is used at early boot for
> power management handling. I don't think it's the case for this
> driver, but I can't be 100% sure.
>
> If you were able to see the flood of WARN_ON's, would be
> interesting to know how it behaves with del_timer(). Mind
> giving it a test?
>
> Thanks,
> Andi

I took some time to take a closer look at this and it turns out that the
timer is used only to exit from the wait_for_completion(), after each
del_timer_sync() there is a complete() call. So I will remove the timer
all together and replace wait_for_completion() with
wait_for_completion_timeout()

--
Piotr Wojtaszczyk
Timesys