On Sun, 27 Aug 2006 13:07:30 +0530
Dipankar Sarma <[email protected]> wrote:
> On Sat, Aug 26, 2006 at 11:46:18PM -0700, Andrew Morton wrote:
> > On Sun, 27 Aug 2006 11:41:55 +0530
> >
> > > The right thing to do would be to
> > > do an audit and clean up the bad lock_cpu_hotplug() calls.
> >
> > No, that won't fix it. For example, take a look at all the *callers* of
> > cpufreq_update_policy(). AFAICT they're all buggy. Fiddling with the
> > existing lock_cpu_hotplug() sites won't fix that. (Possibly this
> > particular problem can be fixed by checking that the relevant CPU is still
> > online after the appropriate locking has been taken - dunno).
> >
>
> This is a different issue from the ones that relates to lock_cpu_hotplug().
Well not really. The thinking goes "gee, we need to lock against CPU
hotplug. THe CPU hotplug guys gave us lock_cpu_hotplug() so we're supposed
to use that somethere". We see the result.
> This one seems like a cpufreq internal locking problem.
>
> On a quick look at this,
Me too. But fixing this will require a long look. What per-cpu resources
are being used? How should they be locked? Implement.
> it seems to me that cpufreq_cpu_get() should
> do exactly what you said - use a spinlock in each cpufreq_cpu_data[] to
> protect the per-cpu flag and in cpufreq_cpu_get() check if
> !data and data->online == 0. They may have to do -
>
> static struct cpufreq_data {
> spinlock_t lock;
> int flag;
> struct cpufreq_policy *policy;
> } cpufreq_cpu_data[NR_CPUS];
>
I think we're agreeing... cpufreq locking is busted, needs to be redone
and, I would suggest, fancifying lock_cpu_hotplug() isn't the way to do it.
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