Re: [PATCH] asm-generic: Use raw_local_irq_save/restore instead local_irq_save/restore

Michal Simek
2010-07-26T08:53:19Z

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Andrew Morton wrote:
> On Wed, 26 May 2010 10:42:43 -0400 Steven Rostedt <rostedt@goodmis.org> wrote:
>
>> On Wed, 2010-05-26 at 10:48 +0200, monstr@monstr.eu wrote:
>>> From: Michal Simek <monstr@monstr.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@monstr.eu>
>> Acked-by: Steven Rostedt <rostedt@goodmis.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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>From 06c2447c8939227b4c4d3340fba1c712f03e70ca Mon Sep 17 00:00:00 2001
From: Michal Simek <monstr@monstr.eu>
Date: Wed, 26 May 2010 08:57:36 +0200
Subject: [PATCH] asm-generic: Use raw_local_irq_save/restore instead local_irq_save/restore

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@monstr.eu>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
include/asm-generic/atomic.h | 12 ++++++------
1 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/include/asm-generic/atomic.h b/include/asm-generic/atomic.h
index 058129e..e53347f 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); /* Don't trace it in a irqsoff handler */
temp = v->counter;
temp += i;
v->counter = temp;
- local_irq_restore(flags);
+ raw_local_irq_restore(flags);

return temp;
}
@@ -78,11 +78,11 @@ static inline int atomic_sub_return(int i, atomic_t *v)
unsigned long flags;
int temp;

- local_irq_save(flags);
+ raw_local_irq_save(flags); /* Don't trace it in a irqsoff handler */
temp = v->counter;
temp -= i;
v->counter = temp;
- local_irq_restore(flags);
+ raw_local_irq_restore(flags);

return temp;
}
@@ -135,9 +135,9 @@ static inline void atomic_clear_mask(unsigned long mask, unsigned long *addr)
unsigned long flags;

mask = ~mask;
- local_irq_save(flags);
+ raw_local_irq_save(flags); /* Don't trace it in a irqsoff handler */
*addr &= mask;
- local_irq_restore(flags);
+ raw_local_irq_restore(flags);
}

#define atomic_xchg(ptr, v) (xchg(&(ptr)->counter, (v)))
--
1.5.5.6