linux-kernel - Re: [patch 16/20] perf/x86/intel: Drop get_online_cpus() in intel_snb_check

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Date:   Tue, 18 Apr 2017 13:27:51 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sebastian Siewior <bigeasy@...utronix.de>, x86@...nel.org
Subject: Re: [patch 16/20] perf/x86/intel: Drop get_online_cpus() in
 intel_snb_check_microcode()

On Sat, Apr 15, 2017 at 07:01:23PM +0200, Thomas Gleixner wrote:
> From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> 
> If intel_snb_check_microcode() is invoked via
>   microcode_init -> perf_check_microcode -> intel_snb_check_microcode
> 
> then get_online_cpus() is invoked nested. This works with the current
> implementation of get_online_cpus() but prevents converting it to a percpu
> rwsem.
> 
> intel_snb_check_microcode() is also invoked from intel_sandybridge_quirk()
> unprotected.
> 
> Drop get_online_cpus() from intel_snb_check_microcode() and add it to
> intel_sandybridge_quirk() so both call sites are protected.
> 
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: x86@...nel.org

Acked-by: Borislav Petkov <bp@...e.de>

-- 
Regards/Gruss,
    Boris.

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