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

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Message-ID: <CACVXFVNNzgMFQ_G7HeF39S7Pz42qsM+0rZaTCSy76y+sXUREUA@mail.gmail.com>
Date:	Wed, 13 Mar 2013 08:57:04 +0800
From:	Ming Lei <tom.leiming@...il.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	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>,
	Christoph Lameter <cl@...ux-foundation.org>
Subject: Re: [PATCH v1] ARM: keep __my_cpu_offset consistent with generic one

On Wed, Mar 13, 2013 at 1:25 AM, Tejun Heo <tj@...nel.org> wrote:
> Hello,
>
> On Tue, Mar 12, 2013 at 07:44:55PM +0800, Ming Lei wrote:
>> On Tue, Mar 12, 2013 at 7:30 PM, Russell King - ARM Linux
>> <linux@....linux.org.uk> wrote:
>> >>
>> >> Ingo and Peter, what is your opinion on the problem?
>> >
>> > Having discussed this with Ben Herrenschmidt, it seems that we do need
>> > to have a more complex patch to sort this out - we need to setup our
>> > private pointer inside setup_per_cpu_areas().
>>
>> Suppose so, seems the patch is still needed to make CPU0 see
>> static variables in '.data..percpu' section correctly.
>
> If my memory serves me right, x86 also has places where CPU0 accesses
> its per-cpu data in .data.percpu.  While those existed (not sure
> they're still there but probably they're) mostly due to historical
> reasons rather than by design, as long as the data is in consistent
> state by and during percpu setup, nothing will break.

Tejun, thanks for your input, yes, nothing will break.  For lockdep,
the percpu variables in non-boot-CPUs may be initialized again after
percpu area is set up.


Thanks,
-- 
Ming Lei
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