RE: was [Re: [PATCH v3] watchdog: Add hrtimer-based pretimeout feature]

["Klein, Curtis" <curtis.klein@hpe.com>]

On 9/4/21, 1:19AM, Jiri Slaby wrote:
> On 04. 09. 21, 10:16, Jiri Slaby wrote:
> > On 02. 09. 21, 16:05, Guenter Roeck wrote:
> >> On 9/1/21 11:55 PM, Jiri Slaby wrote:
> >>> On 03. 02. 21, 21:11, Curtis Klein wrote:
> >>>> This adds the option to use a hrtimer to generate a watchdog pretimeout
> >>>> event for hardware watchdogs that do not natively support watchdog
> >>>> pretimeouts.
> >>>>
> >>>> With this enabled, all watchdogs will appear to have pretimeout support
> >>>> in userspace. If no pretimeout value is set, there will be no change in
> >>>> the watchdog's behavior.
> >>>
> >>> Hi,
> >>>
> >>> on my Dell Latitude 7280, CONFIG_WATCHDOG_HRTIMER_PRETIMEOUT=y causes
> >>> all reboot, kexec, suspend to panic. Disabling that option makes it
> >>> all work again. Provided it happens very late in the process, I don't
> >>> know how to grab some logs...
> >>>
> >>> Any ideas?
> >>>
> >>
> >> AFAICS the timer does not stop on reboot. I think we'll need to
> >> augment the code
> >> to do that.
> >
> > No, it is stopped via device unregister -> watchdog_dev_unregister ->
> > watchdog_cdev_unregister -> watchdog_hrtimer_pretimeout_stop.
> >
> > But look:
> > watchdog_cdev_unregister
> >    -> wdd->wd_data = NULL;
> >    -> watchdog_hrtimer_pretimeout_stop
> >      -> hrtimer_cancel(&wdd->wd_data->pretimeout_timer);
> >
> > The diff below obviously fixes the issue,
> 
> Which is exactly a -next commit:
> commit c7b178dae139f8857edc50888cfbf251cd974a38
> Author: Curtis Klein <curtis.klein@hpe.com>
> Date:   Tue Jun 22 23:26:23 2021 -0700
> 
>      watchdog: Fix NULL pointer dereference when releasing cdev
> 
> > --- a/drivers/watchdog/watchdog_dev.c
> > +++ b/drivers/watchdog/watchdog_dev.c
> > @@ -1096,6 +1096,8 @@ static void watchdog_cdev_unregister(struct
> > watchdog_device *wdd)
> >                  watchdog_stop(wdd);
> >          }
> >
> > +       watchdog_hrtimer_pretimeout_stop(wdd);
> > +
> >          mutex_lock(&wd_data->lock);
> >          wd_data->wdd = NULL;
> >          wdd->wd_data = NULL;
> > @@ -1103,7 +1105,6 @@ static void watchdog_cdev_unregister(struct
> > watchdog_device *wdd)
> >
> >          hrtimer_cancel(&wd_data->timer);
> >          kthread_cancel_work_sync(&wd_data->work);
> > -       watchdog_hrtimer_pretimeout_stop(wdd);
> >
> >          put_device(&wd_data->dev);
> >   }
> >
> > thanks,
> 
> 
> --
> js
> suse labs

Does it still make sense to stop the timer on reboot or suspend?

I haven't had any problems with rebooting but I haven't been able to test
suspending.

-Curtis