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

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Date:	Wed, 28 Jul 2010 07:20:43 +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, linux-arch@...r.kernel.org
Subject: Re: [PATCH] asm-generic: Use raw_local_irq_save/restore instead local_irq_save/restore

Andrew Morton wrote:
> On Mon, 26 Jul 2010 10:49:50 +0200
> Michal Simek <monstr@...str.eu> wrote:
> 
>> 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.
> 
> Seems that this will also affect blackfin, mn10300 and score.  I guess
> they aren't supporting tracing yet?

If they uses asm-generic/atomic.h, then yes. It seems to me that 
Blackfin uses own asm/atomic.h. nm10300 and score are the same case as 
Microblaze.

In include/linux/irqflags.h is written this commentary.

/*
  * The local_irq_*() APIs are equal to the raw_local_irq*()
  * if !TRACE_IRQFLAGS.
  */

If architecture doesn't enable TRACE_IRQFLAGS then there is no 
difference in behavior. If yes and use asm-generic/atomic.h code, then 
IRQFLAG tracer freeze because it is traced part of irqsoff tracer 
because of recursion as is describe in patch description.

> 
>> Signed-off-by: Michal Simek <monstr@...str.eu>
>> Acked-by: Steven Rostedt <rostedt@...dmis.org>
>> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> 
> hm, I wonder how my signoff got there.  Doesn't matter.

http://lkml.org/lkml/2010/5/26/364

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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