linux-kernel - Re: [PATCH] asm-generic: Use raw_local_irq_save/restore instead local_irq

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Message-ID: <4C4D4C2E.8010103@monstr.eu>
Date:	Mon, 26 Jul 2010 10:49:50 +0200
From:	Michal Simek <monstr@...str.eu>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	rostedt@...dmis.org, linux-kernel@...r.kernel.org,
	tglx@...utronix.de, mingo@...e.hu
Subject: Re: [PATCH] asm-generic: Use raw_local_irq_save/restore instead local_irq_save/restore

Andrew Morton wrote:
> On Wed, 26 May 2010 10:42:43 -0400 Steven Rostedt <rostedt@...dmis.org> wrote:
> 
>> On Wed, 2010-05-26 at 10:48 +0200, monstr@...str.eu wrote:
>>> From: Michal Simek <monstr@...str.eu>
>>>
>>> start/stop_critical_timing function for preemptirqsoff, preemptoff
>>> and irqsoff tracers contains atomic_inc and atomic_dec operations.
>>>
>>> Atomic operations used local_irq_save/restore macros to ensure
>>> atomic access but they are traced by the same function which is causing
>>> recursion problem.
>>>
>>> The reason is when these tracers are turn ON then local_irq_save/restore
>>> macros are changed in include/linux/irqflags.h to call trace_hardirqs_on/off
>>> which call start/stop_critical_timing.
>>>
>>> Microblaze was affected because use generic atomic implementation.
>>>
>>> Signed-off-by: Michal Simek <monstr@...str.eu>
>> Acked-by: Steven Rostedt <rostedt@...dmis.org>
>>
> 
> Sighed-at-by: me.
> 
>>> diff --git a/include/asm-generic/atomic.h b/include/asm-generic/atomic.h
>>> index 058129e..6c190fd 100644
>>> --- a/include/asm-generic/atomic.h
>>> +++ b/include/asm-generic/atomic.h
>>> @@ -57,11 +57,11 @@ static inline int atomic_add_return(int i, atomic_t *v)
>>>  	unsigned long flags;
>>>  	int temp;
>>>  
>>> -	local_irq_save(flags);
>>> +	raw_local_irq_save(flags);
>>>  	temp = v->counter;
>>>  	temp += i;
>>>  	v->counter = temp;
>>> -	local_irq_restore(flags);
>>> +	raw_local_irq_restore(flags);
>>>  
>>>  	return temp;
>>>  }
> 
> If a developer looks at atomic_add_return() and asks himself "why did
> this use raw_local_irq_save()", the only way of answering that question
> is to go groveling through the git logs, which is a right PITA if
> you're trying to get some coding work done.
> 
> Guys, any time you add code which is non-obvious at the raw C level, it
> *needs* a comment!

Andrew: Can you please add this patch to your tree? I have it in 
microblaze next branch but should go through different tree.

Thanks,
Michal

-- 
Michal Simek, Ing. (M.Eng)
w: www.monstr.eu p: +42-0-721842854
Maintainer of Linux kernel 2.6 Microblaze Linux - http://www.monstr.eu/fdt/
Microblaze U-BOOT custodian

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