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SubjectRe: [patch 00/61] ANNOUNCE: lock validator -V1
Hi,

On Tue, May 30, 2006 at 10:58:52AM -0400, Dave Jones wrote:
> On Tue, May 30, 2006 at 04:19:22PM +0200, Arjan van de Ven wrote:
>
> > > > One
> > > > ---
> > > > store_scaling_governor takes policy->lock and then calls __cpufreq_set_policy
> > > > __cpufreq_set_policy calls __cpufreq_governor
> > > > __cpufreq_governor calls __cpufreq_driver_target via cpufreq_governor_performance
> > > > __cpufreq_driver_target calls lock_cpu_hotplug() (which takes the hotplug lock)
> > > >
> > > >
> > > > Two
> > > > ---
> > > > cpufreq_stats_init lock_cpu_hotplug() and then calls cpufreq_stat_cpu_callback
> > > > cpufreq_stat_cpu_callback calls cpufreq_update_policy
> > > > cpufreq_update_policy takes the policy->lock
> > > >
> > > >
> > > > so this looks like a real honest AB-BA deadlock to me...
> > >
> > > This looks a little clearer this morning. I missed the fact that sys_init_module
> > > isn't completely serialised, only the loading part. ->init routines can and will be
> > > called in parallel.
> > >
> > > I don't see where cpufreq_update_policy takes policy->lock though.
> > > In my tree it just takes the per-cpu data->lock.
> >
> > isn't that basically the same lock?
>
> Ugh, I've completely forgotten how this stuff fits together.
>
> Dominik, any clues ?

That's indeed a possible deadlock situation -- what's the
cpufreq_update_policy() call needed for in cpufreq_stat_cpu_callback anyway?

Dominik
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