linux-kernel - Re: [PATCH 4/4] ring-buffer: change WARN_ON from checking preempt

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Date:	Thu, 7 May 2009 21:54:27 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH 4/4] ring-buffer: change WARN_ON from checking
 preempt_count to preemptible

On Fri, 08 May 2009 00:32:54 -0400 Steven Rostedt <rostedt@...dmis.org> wrote:

> From: Steven Rostedt <srostedt@...hat.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@...dmis.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.
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