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

From: Ming Lei
Date: Mon Mar 11 2013 - 22:32:27 EST

On Thu, Mar 7, 2013 at 9:35 PM, Ming Lei <tom.leiming@xxxxxxxxx> 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@xxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Rob Herring <rob.herring@xxxxxxxxxxx>
> Cc: Will Deacon <will.deacon@xxxxxxx>
> Cc: Nicolas Pitre <nico@xxxxxxxxxx>
> Cc: Russell King <rmk+kernel@xxxxxxxxxxxxxxxx>
> Signed-off-by: Ming Lei <tom.leiming@xxxxxxxxx>
> ---
> 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

Ming Lei
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