Re: [PATCH v1 2/2] x86, perf,cqm: handle CPU hotplug

[Vikas Shivappa]

On Thu, 18 Jun 2015, Thomas Gleixner wrote:

> On Thu, 18 Jun 2015, Kanaka Juvva wrote:
>
> > Added lock in event reader function. The cqm_pick_event_reader() function
> > accesses cqm_cpumask and it is critical section between this and
> > cqm_stable().
> >
> > This situation is true when a CPU is hotplugged. Mutex is used to protect
> > the critical section.
> >
> > Signed-off-by: Kanaka Juvva <kanaka.d.juvva@xxxxxxxxxxxxxxx>
> > ---
> >  arch/x86/kernel/cpu/perf_event_intel_cqm.c | 5 ++++-
> >  1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/kernel/cpu/perf_event_intel_cqm.c b/arch/x86/kernel/cpu/perf_event_intel_cqm.c
> > index 1880761..e17e37f 100644
> > --- a/arch/x86/kernel/cpu/perf_event_intel_cqm.c
> > +++ b/arch/x86/kernel/cpu/perf_event_intel_cqm.c
> > @@ -1239,12 +1239,15 @@ static inline void cqm_pick_event_reader(int cpu)
> >  	int phys_id = topology_physical_package_id(cpu);
> >  	int i;
> >
> > +	mutex_lock(&cache_mutex);
>
> I already explained it to Vikas. You CANNOT take a mutex in that code
> path as it runs with interrupts disabled on a CPU which cannot
> schedule.

This patch also needs to be merged with the new package mask changes that 
was added. 
Will merge and send the fix.

Thanks,
Vikas

> Sigh.
>
> 	tglx
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