Re: [PATCH 1/2] watchdog: introduce watchdog_dev_suspend/resume

[Grzegorz Jaszczyk <grzegorz.jaszczyk@linaro.org>]

On Tue, 15 Jun 2021 at 16:18, Guenter Roeck <linux@roeck-us.net> wrote:
>
> On Tue, Jun 15, 2021 at 02:39:03PM +0200, Grzegorz Jaszczyk wrote:
> > The watchdog drivers often disable wdog clock during suspend and then
> > enable it again during resume. Nevertheless the ping worker is still
> > running and can issue low-level ping while the wdog clock is disabled
> > causing the system hang. To prevent such condition introduce
> > watchdog_dev_suspend/resume which can be used by any wdog driver and
> > actually cancel ping worker during suspend and restore it back, if
> > needed, during resume.
> >
>
> I'll have to look into this further, but I don't think this is the correct
> solution. Most likely the watchdog core needs to have its own independent
> suspend/resule functions and suspend the high resolution timer on
> suspend and restore it on resume. This may require an additional flag
> to be set by drivers to indicate that the timer should be stopped on
> suspend.

That makes sense - thank you for your suggestion. I think I could
register a pm notifier in the watchdog core when the new e.g.
WDOG_STOP_PING_ON_SUSPEND status flag will be set by the driver and
actually call watchdog_dev_suspend/resume from the notifier callback.
Please let me know if you see any other issue with this solution, if
not I will post v2.

Thank you in advance,
Grzegorz




>
> > Signed-off-by: Grzegorz Jaszczyk <grzegorz.jaszczyk@linaro.org>
> > ---
> >  drivers/watchdog/watchdog_dev.c | 49 +++++++++++++++++++++++++++++++++
> >  include/linux/watchdog.h        |  2 ++
> >  2 files changed, 51 insertions(+)
> >
> > diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
> > index 2946f3a63110..3feca1567281 100644
> > --- a/drivers/watchdog/watchdog_dev.c
> > +++ b/drivers/watchdog/watchdog_dev.c
> > @@ -1219,6 +1219,55 @@ void __exit watchdog_dev_exit(void)
> >       kthread_destroy_worker(watchdog_kworker);
> >  }
> >
> > +int watchdog_dev_suspend(struct watchdog_device *wdd)
> > +{
> > +     struct watchdog_core_data *wd_data = wdd->wd_data;
> > +     int ret;
> > +
> > +     if (!wdd->wd_data)
> > +             return -ENODEV;
> > +
> > +     /* ping for the last time before suspend */
> > +     mutex_lock(&wd_data->lock);
> > +     if (watchdog_worker_should_ping(wd_data))
> > +             ret = __watchdog_ping(wd_data->wdd);
> > +     mutex_unlock(&wd_data->lock);
> > +
> > +     if (ret)
> > +             return ret;
> > +
> > +     /*
> > +      * make sure that watchdog worker will not kick in when the wdog is
> > +      * suspended
> > +      */
> > +     hrtimer_cancel(&wd_data->timer);
> > +     kthread_cancel_work_sync(&wd_data->work);
> > +
> > +     return 0;
> > +}
> > +EXPORT_SYMBOL_GPL(watchdog_dev_suspend);
> > +
> > +int watchdog_dev_resume(struct watchdog_device *wdd)
> > +{
> > +     struct watchdog_core_data *wd_data = wdd->wd_data;
> > +     int ret;
> > +
> > +     if (!wdd->wd_data)
> > +             return -ENODEV;
> > +
> > +     /*
> > +      * __watchdog_ping will also retrigger hrtimer and therefore restore the
> > +      * ping worker if needed.
> > +      */
> > +     mutex_lock(&wd_data->lock);
> > +     if (watchdog_worker_should_ping(wd_data))
> > +             ret = __watchdog_ping(wd_data->wdd);
> > +     mutex_unlock(&wd_data->lock);
> > +
> > +     return ret;
> > +}
> > +EXPORT_SYMBOL_GPL(watchdog_dev_resume);
> > +
> >  module_param(handle_boot_enabled, bool, 0444);
> >  MODULE_PARM_DESC(handle_boot_enabled,
> >       "Watchdog core auto-updates boot enabled watchdogs before userspace takes over (default="
> > diff --git a/include/linux/watchdog.h b/include/linux/watchdog.h
> > index 9b19e6bb68b5..febfde3b1ff6 100644
> > --- a/include/linux/watchdog.h
> > +++ b/include/linux/watchdog.h
> > @@ -209,6 +209,8 @@ extern int watchdog_init_timeout(struct watchdog_device *wdd,
> >                                 unsigned int timeout_parm, struct device *dev);
> >  extern int watchdog_register_device(struct watchdog_device *);
> >  extern void watchdog_unregister_device(struct watchdog_device *);
> > +int watchdog_dev_suspend(struct watchdog_device *wdd);
> > +int watchdog_dev_resume(struct watchdog_device *wdd);
> >
> >  int watchdog_set_last_hw_keepalive(struct watchdog_device *, unsigned int);
> >
> > --
> > 2.29.0
> >