Re: [PATCH 4/4] ring-buffer: change WARN_ON from checkingpreempt_count to preemptible

From: Ingo Molnar
Date: Fri May 08 2009 - 07:31:57 EST



* Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:

>
>
> On Thu, 7 May 2009, Andrew Morton wrote:
>
> > On Fri, 08 May 2009 00:32:54 -0400 Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
> >
> > > From: Steven Rostedt <srostedt@xxxxxxxxxx>
> > >
> > > There's a WARN_ON in the ring buffer code that makes sure preemption
> > > is disabled. It checks "!preempt_count()". But when CONFIG_PREEMPT is not
> > > enabled, preempt_count() is always zero, and this will trigger the warning.
> > >
> > > [ Impact: prevent false warning on non preemptible kernels ]
> > >
> > > Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
> > > ---
> > > kernel/trace/ring_buffer.c | 2 +-
> > > 1 files changed, 1 insertions(+), 1 deletions(-)
> > >
> > > diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> > > index 3ae5ccf..3611706 100644
> > > --- a/kernel/trace/ring_buffer.c
> > > +++ b/kernel/trace/ring_buffer.c
> > > @@ -1688,7 +1688,7 @@ void ring_buffer_discard_commit(struct ring_buffer *buffer,
> > > * committed yet. Thus we can assume that preemption
> > > * is still disabled.
> > > */
> > > - RB_WARN_ON(buffer, !preempt_count());
> > > + RB_WARN_ON(buffer, preemptible());
> > >
> > > cpu = smp_processor_id();
> > > cpu_buffer = buffer->buffers[cpu];
> >
> > smp_processor_id() will warn too.
> >
>
> The difference is that RB_WARN_ON also disables the ring buffer.

Yes, it's a more robust form of warning, in this context.

Ingo
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