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

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Date:	Tue, 16 Jun 2015 21:25:20 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Vikas Shivappa <vikas.shivappa@...el.com>
cc:	Vikas Shivappa <vikas.shivappa@...ux.intel.com>,
	linux-kernel@...r.kernel.org, x86@...nel.org, hpa@...or.com,
	mingo@...nel.org, peterz@...radead.org, matt.fleming@...el.com,
	will.auld@...el.com, linux-rdt@...ists.intel.com
Subject: Re: [PATCH 09/10] x86/intel_rdt: Hot cpu support for Cache
 Allocation

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?

Thanks,

	tglx
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