Re: [PATCH -tip V2] ring_buffer: fix warning

Frederic Weisbecker
2009-07-16T16:11:04Z

On Wed, Jul 15, 2009 at 04:27:30PM +0800, Lai Jiangshan wrote:
> Sorry for missing Reviewed-by and Acked-by, so I resend it.
>
> Subject: [PATCH -tip V2] ring_buffer: fix warning
>
> kernel/trace/ring_buffer.c: In function 'rb_tail_page_update':
> kernel/trace/ring_buffer.c:849: warning: value computed is not used
> kernel/trace/ring_buffer.c:850: warning: value computed is not used
>
> Add "(void)"s to fix this warning.
>
> Changed from V1:
> Add a comment(which is written by Steven) for it.
>
> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
> Reviewed-by: Frederic Weisbecker <fweisbec@gmail.com>
> Acked-by: Steven Rostedt <rostedt@goodmis.org>

Queued for .32, thanks!

> ---
> diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> index e648ba4..51633d7 100644
> --- a/kernel/trace/ring_buffer.c
> +++ b/kernel/trace/ring_buffer.c
> @@ -845,9 +845,14 @@ static int rb_tail_page_update(struct ring_buffer_per_cpu *cpu_buffer,
> * This will only succeed if an interrupt did
> * not come in and change it. In which case, we
> * do not want to modify it.
> + *
> + * We add (void) to let the compiler know that we do not care
> + * about the return value of these functions. We use the
> + * cmpxchg to only update if an interrupt did not already
> + * do it for us. If the cmpxchg fails, we don't care.
> */
> - local_cmpxchg(&next_page->write, old_write, val);
> - local_cmpxchg(&next_page->entries, old_entries, eval);
> + (void)local_cmpxchg(&next_page->write, old_write, val);
> + (void)local_cmpxchg(&next_page->entries, old_entries, eval);
>
> /*
> * No need to worry about races with clearing out the commit.
>