linux-kernel - Re: [PATCH 2/3] perf_events: fix validation of events using an extra reg (v4)

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Message-ID: <BANLkTimSO-+-0=bc=TZqvUxe7gwsSn1xRg@mail.gmail.com>
Date:	Thu, 9 Jun 2011 22:36:10 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	"mingo@...e.hu" <mingo@...e.hu>, Andi Kleen <andi@...stfloor.org>,
	Lin Ming <ming.m.lin@...el.com>
Subject: Re: [PATCH 2/3] perf_events: fix validation of events using an extra
 reg (v4)

On Thu, Jun 9, 2011 at 8:40 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Mon, 2011-06-06 at 16:57 +0200, Stephane Eranian wrote:
>> +static struct cpu_hw_events *allocate_fake_cpuc(void)
>> +{
>> +       struct cpu_hw_events *cpuc;
>> +       int cpu = smp_processor_id();
>
> That's a boo-boo, clearly we are in a preemptible context here (see the
> GFP_KERNEL allocation on the next line), so using smp_processor_id()
> isn't valid.
>
Good point. I missed that.

> Now since all that allocate_shared_regs() does with it is pick a NUMA
> node, we should probably use raw_smp_processor_id() and leave it at
> that, right?
>
Yeah, for what we do with fake_cpuc, it does not really matter where
it comes from. This is not on any critical path. The simplest allocator
will do it.


>> +       cpuc = kzalloc(sizeof(*cpuc), GFP_KERNEL);
>> +       if (!cpuc)
>> +               return ERR_PTR(-ENOMEM);
>> +
>> +       /* only needed, if we have extra_regs */
>> +       if (x86_pmu.extra_regs) {
>> +               cpuc->shared_regs = allocate_shared_regs(cpu);
>> +               if (!cpuc->shared_regs)
>> +                       goto error;
>> +       }
>> +       return cpuc;
>> +error:
>> +       free_fake_cpuc(cpuc);
>> +       return ERR_PTR(-ENOMEM);
>> +}
>
>
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