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From: Steven Rostedt on 26 May 2010 10:50
On Wed, 2010-05-26 at 10:48 +0200, monstr(a)monstr.eu wrote:
> From: Michal Simek <monstr(a)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(a)monstr.eu>

Acked-by: Steven Rostedt <rostedt(a)goodmis.org>

-- Steve

> ---
> 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..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;
> }
> @@ -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);
> 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);
> *addr &= mask;
> - local_irq_restore(flags);
> + raw_local_irq_restore(flags);
> }
>
> #define atomic_xchg(ptr, v) (xchg(&(ptr)->counter, (v)))


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From: Andrew Morton on 26 May 2010 13:10
On Wed, 26 May 2010 10:42:43 -0400 Steven Rostedt <rostedt(a)goodmis.org> wrote:

> On Wed, 2010-05-26 at 10:48 +0200, monstr(a)monstr.eu wrote:
> > From: Michal Simek <monstr(a)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(a)monstr.eu>
>
> Acked-by: Steven Rostedt <rostedt(a)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!
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From: Steven Rostedt on 26 May 2010 13:20
On Wed, 2010-05-26 at 10:08 -0700, Andrew Morton wrote:

>
> 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!

Totally agree! I've gotten pretty good at adding comments to changes
like this that I do. I need to get better at telling others to comment
their work ;-)

-- Steve



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