linux-kernel - Re: [PATCH UPDATED#3 04/16] x86: setup_local_APIC() must always be called with preemption disabled

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Date:	Thu, 09 Dec 2010 18:18:54 +0200
From:	Pekka Enberg <penberg@...nel.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	linux-kernel@...r.kernel.org, mingo@...hat.com, tglx@...utronix.de,
	hpa@...or.com, x86@...nel.org, eric.dumazet@...il.com,
	yinghai@...nel.org, brgerst@...il.com, gorcunov@...il.com
Subject: Re: [PATCH UPDATED#3 04/16] x86: setup_local_APIC() must always be
 called with preemption disabled

On Thu, 2010-12-09 at 11:47 +0100, Tejun Heo wrote:
> setup_local_APIC() is used to setup local APIC early during CPU
> initialization and already assumes that preemption is disabled on
> entry.  However, The function unnecessarily disables and enables
> preemption and uses smp_processor_id() multiple times in and out of
> the nested preemption disabled section.  This gives the wrong
> impression that the function might be able to handle being called with
> preemption enabled and/or migrated to another processor in the middle.
> 
> Make it clear that the function is always called with preemption
> disabled, drop the confusing preemption disable block and call
> smp_processor_id() once at the beginning of the function.
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Cc: Yinghai Lu <yinghai@...nel.org>
> Cc: Cyrill Gorcunov <gorcunov@...il.com>
> Cc: Pekka Enberg <penberg@...nel.org>

Reviewed-by: Pekka Enberg <penberg@...nel.org>

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