linux-kernel - Re: [PATCH v1] ARM: keep __my_cpu_offset consistent with generic one

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Message-ID: <CACVXFVOhr222CVrzkVP_oLgVkdReD9BXXSBg7fmp6Wvx9_peCw@mail.gmail.com>
Date:	Tue, 12 Mar 2013 10:32:21 +0800
From:	Ming Lei <tom.leiming@...il.com>
To:	linux-arm-kernel@...ts.infradead.org
Cc:	linux-kernel@...r.kernel.org, Ming Lei <tom.leiming@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Rob Herring <rob.herring@...xeda.com>,
	Will Deacon <will.deacon@....com>,
	Nicolas Pitre <nico@...aro.org>,
	Russell King <rmk+kernel@....linux.org.uk>
Subject: Re: [PATCH v1] ARM: keep __my_cpu_offset consistent with generic one

On Thu, Mar 7, 2013 at 9:35 PM, Ming Lei <tom.leiming@...il.com> wrote:
> Commit 14318efb(ARM: 7587/1: implement optimized percpu variable access)
> introduces arm's __my_cpu_offset to optimize percpu vaiable access,
> which really works well on hackbench, but will cause __my_cpu_offset
> to return garbage value before it is initialized in cpu_init() called
> by setup_arch, so accessing percpu variable before setup_arch may cause
> kernel hang. But generic __my_cpu_offset always returns zero before
> percpu area is brought up, and won't hang kernel.
>
> So the patch tries to clear __my_cpu_offset on boot CPU early
> to avoid boot hang.
>
> At least now percpu variable is accessed by lockdep before
> setup_arch(), and enabling CONFIG_LOCK_STAT or CONFIG_DEBUG_LOCKDEP
> can trigger kernel hang.
>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Rob Herring <rob.herring@...xeda.com>
> Cc: Will Deacon <will.deacon@....com>
> Cc: Nicolas Pitre <nico@...aro.org>
> Cc: Russell King <rmk+kernel@....linux.org.uk>
> Signed-off-by: Ming Lei <tom.leiming@...il.com>
> ---
> V1:
>         - documents lockdep uses percpu variable early

Looks no one objects the patch, so I has submitted it into Russell's
patch system, and hope it can be pushed to linus tree soon and
make LOCK_STAT/DEBUG_LOCKDEP usable on ARMv7.


Thanks,
-- 
Ming Lei
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