Re: timers vs drivers suspend race

["Janusz Użycki" <j.uzycki@elproma.com.pl>]

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W dniu 2014-09-19 13:23, Janusz Użycki pisze:
> Hi.
>
> I have a doubt about suspending of timers.
> I found the patch (not included to linux-next):
> https://lkml.org/lkml/2014/7/21/493
> but it concerns timers only.
>
> I'm adding PM to the watchdog driver (below).
> The driver is capable to stop the watchdog.
> However I implemented "keep-on" feature to ping
> active watchdog if userland doesn't do it.
> For the feature I used a timer.
> Now, on wdt_suspend() call I don't know
> if timers are suspended before the watchdog driver or
> there is no guarantee (race): wdt_suspend() calls wdt_stop()
> and after timer's callback will ping watchdog and reenable it.
>
> I found also:
> https://lkml.org/lkml/2007/10/25/9
> Here del_timer_sync() is called and it solves
> the problem.
> In my case the timer is serviced in watchdog_dev,
> not in the specific-driver.
> I can add a flag in the specific-driver
> to block watchdog's ping before wdt_stop()
> or export new function to suspend/resume
> watchdog_dev's timer from the specific-driver.
>
> Could you advice is it necessary?

Does changing SIMPLE_DEV_PM_OPS to SET_LATE_SYSTEM_SLEEP_PM_OPS
solve the race problem with timer?

best regards
Janusz



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