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

Steven Rostedt
2009-05-08T10:53:58Z

On Thu, 7 May 2009, Andrew Morton wrote:

> On Fri, 08 May 2009 00:32:54 -0400 Steven Rostedt <rostedt@goodmis.org> wrote:
>
> > From: Steven Rostedt <srostedt@redhat.com>
> >
> > 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@goodmis.org>
> > ---
> > 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.

-- Steve