On Fri, 5 Jul 2013, Alex Shi wrote:
> On 07/04/2013 09:04 PM, Thomas Gleixner wrote:
> >>> > > static int clocksource_watchdog_kthread(void *data)
> >>> > > {
> >>> > > struct clocksource *cs, *tmp;
> >>> > > @@ -412,11 +415,14 @@ static int clocksource_watchdog_kthread(void
> >>> > > *data)
> >>> > >
> >>> > > mutex_lock(&clocksource_mutex);
> >>> > > spin_lock_irqsave(&watchdog_lock, flags);
> >>> > > - list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list)
> >>> > > + list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list) {
> >>> > > if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
> >>> > > list_del_init(&cs->wd_list);
> >>> > > list_add(&cs->wd_list, &unstable);
> >>> > > }
> >>> > > + if (cs->flags & CLOCK_SOURCE_VALID_FOR_HRES)
> >>> > > + clocksource_select();
> >> >
> >> > Unlikely, but if we have 3 watched clocksources which have the HRES
> >> > bit set, you'd call 3 times clocksource_select().
> > Also the reselect must be called outside the watchdog_lock region.
>
> Sorry for stupid, the watchdog_lock used protect watchdog related
> resource. but clocksource_select doesn't touch them. So, I know it isn't
> necessary to put reselect under this lock. Just don't know why the
> reselect *must* be called outside of it?
clocksource_select()
timekeeping_notify()
stop_machine()
get_online_cpus()
might_sleep()
mutex_lock()
So we need to be in preemptible context when we call clocksource_select().
Thanks,
tglx
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