Re: [PATCH 09/10] x86/intel_rdt: Hot cpu support for Cache Allocation

[Vikas Shivappa]

On Tue, 16 Jun 2015, Thomas Gleixner wrote:

> On Tue, 16 Jun 2015, Vikas Shivappa wrote:
> > On Tue, 16 Jun 2015, Thomas Gleixner wrote:
> >
> > > On Fri, 12 Jun 2015, Vikas Shivappa wrote:
> > > > +static inline void intel_rdt_cpu_start(int cpu)
> > > > +{
> > > > +	struct intel_pqr_state *state = &per_cpu(pqr_state, cpu);
> > > > +
> > > > +	state->closid = 0;
> > > > +	mutex_lock(&rdt_group_mutex);
> > >
> > > This is called from CPU_STARTING, which runs on the starting cpu with
> > > interrupts disabled. Clearly never tested with any of the mandatory
> > > debug configs enabled.
> >
> > But this can race with cbm_update_all calling on_each_cpu_mask ? or in other
> > words the lock helps on_each_cpu_mask not race with hot cpu code updating the
> > rdt_cpumask since the on_each_cpu_mask is also called with the lock always.
> >
> > Its tested on the 0 day build which should include the debug config. Will add
> > a tested tag.
>
> And that tag gives you special permission to take a mutex in irq
> disabled context on a cpu which cannot schedule, right?

Will fix.

Doing
	case CPU_ONLINE:
		intel_rdt_cpu_start(cpu);
instead of
	CPU_UP_PREPARE:
		intel_rdt_cpu_start(cpu);

should work ?

CPU_ONLINE is just enough for me which doesnot have interrupts 
disabled and i can then sync using the lock.

Thanks,
Vikas

> Thanks,
>
> 	tglx
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