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SubjectRe: [patch 00/15] clocksource / timekeeping rework V4 (resend V3 + bug fix)
On Sat, 15 Aug 2009 12:08:35 +0200 (CEST)
Thomas Gleixner <tglx@linutronix.de> wrote:

> Yeah, we need to call clocksource_change_rating() outside of watchdog
> lock. Spotted a missing _irqrestore as well.
>
> Thanks,
>
> tglx
> ---
>
> diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
> index a1657b5..02dc22d 100644
> --- a/kernel/time/clocksource.c
> +++ b/kernel/time/clocksource.c
> @@ -307,16 +307,23 @@ static void clocksource_watchdog_work(struct work_struct *work)
> {
> struct clocksource *cs, *tmp;
> unsigned long flags;
> + LIST_HEAD(unstable);
>
> spin_lock_irqsave(&watchdog_lock, flags);
> list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list)
> if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
> list_del_init(&cs->wd_list);
> - clocksource_change_rating(cs, 0);
> + list_add(&cs->wd_list, &unstable);
> }
> /* Check if the watchdog timer needs to be stopped. */
> clocksource_stop_watchdog();
> - spin_unlock(&watchdog_lock);
> + spin_unlock_irqrestore(&watchdog_lock, flags);
> +
> + /* Needs to be done outside of watchdog lock */
> + list_for_each_entry_safe(cs, tmp, &unstable, wd_list) {
> + list_del_init(&cs->wd_list);
> + clocksource_change_rating(cs, 0);
> + }
> }
>
> #else /* CONFIG_CLOCKSOURCE_WATCHDOG */

Autsch, the s/spin_unlock/spin_unlock_irqrestore/ is rather obvious, no?
In theory we now have a reference count problem. The call to
clocksource_change_rating are no done outside of the clocksource mutex
and outside of the watchdog lock. A concurrent clocksource_unregister
could remove the clock.

--
blue skies,
Martin.

"Reality continues to ruin my life." - Calvin.



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