On Mon, 9 Apr 2007 22:31:08 -0400 Dave Jones <[email protected]> wrote:
> On Mon, Apr 09, 2007 at 05:26:51PM -0700, Andrew Morton wrote:
> > On Thu, 5 Apr 2007 16:50:34 -0400
> > Dave Jones <[email protected]> wrote:
> >
> > > diff --git a/arch/i386/kernel/cpu/cpufreq/speedstep-centrino.c b/arch/i386/kernel/cpu/cpufreq/speedstep-centrino.c
> > > index f43b987..824d0a2 100644
> > > --- a/arch/i386/kernel/cpu/cpufreq/speedstep-centrino.c
> > > +++ b/arch/i386/kernel/cpu/cpufreq/speedstep-centrino.c
> > > @@ -708,6 +708,7 @@ static int centrino_target (struct cpufreq_policy *policy,
> > > saved_mask = current->cpus_allowed;
> > > first_cpu = 1;
> > > cpus_clear(covered_cpus);
> > > + preempt_disable();
> > > for_each_cpu_mask(j, online_policy_cpus) {
> > > /*
> > > * Support for SMP systems.
> > > @@ -798,6 +799,7 @@ static int centrino_target (struct cpufreq_policy *policy,
> > > }
> > >
> > > migrate_end:
> > > + preempt_enable();
> > > set_cpus_allowed(current, saved_mask);
> > > return 0;
> > > }
> >
> > This means we'll call set_cpus_allowed() while in atomic state, but
> > set_cpus_allowed() does sleepy stuff.
>
> Puzzled. This diff shouldn't change anything about the context we're in
> when we call set_cpus_allowed, and as we're not seeing warnings now,
> I'm not sure what I'm missing?
set_cpus_allowed() will only sleep in special circumstances: when we're
telling the target task that it is not allwed to run on a CPU upon which it
is presently executing. So it needs to be synchronously migrated off that
CPU, which requires that the set_cpus_allowed() caller block.
You're probably just not hitting that case.
Probably we should have a might_sleep() in set_cpus_allowed(), although
there might be callers who are guaranteeed to never hit that case and who
might legitimately want special treatment to avoid the warning.
> [which may be 'the obvious', you wouldn't believe the evening I've had
> involving gas leaks and noxious fumes. Wheee, floaty head.]
Yeah, I get a lot of patches like that.
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