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

From: Michal Simek
Date: Mon Jul 26 2010 - 04:53:23 EST

This is a multi-part message in MIME format.Andrew Morton wrote:
On Wed, 26 May 2010 10:42:43 -0400 Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:

On Wed, 2010-05-26 at 10:48 +0200, monstr@xxxxxxxxx wrote:
From: Michal Simek <monstr@xxxxxxxxx>

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@xxxxxxxxx>
Acked-by: Steven Rostedt <rostedt@xxxxxxxxxxx>

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.


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