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    SubjectRe: [PATCH -tip] ring_buffer: fix warning


    On Tue, 14 Jul 2009, Frederic Weisbecker wrote:

    > On Tue, Jul 14, 2009 at 03:35:37PM +0800, Lai Jiangshan wrote:
    > >
    > > 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 a "(void)" to fix this warning.
    > >
    > > Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
    > > ---
    > > diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
    > > index e648ba4..d371279 100644
    > > --- a/kernel/trace/ring_buffer.c
    > > +++ b/kernel/trace/ring_buffer.c
    > > @@ -846,8 +846,8 @@ static int rb_tail_page_update(struct ring_buffer_per_cpu *cpu_buffer,
    > > * not come in and change it. In which case, we
    > > * do not want to modify it.
    > > */
    > > - 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.
    >
    >
    > Looks good. Indeed the rest of the path remains the same, whether the
    > interrupts have already won the race or not.

    Yes, but it needs a comment:

    /*
    * 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.
    */

    Then you can have my:

    Acked-by: Steven Rostedt <rostedt@goodmis.org>

    -- Steve

    >
    > Reviewed-by: Frederic Weisbecker <fweisbec@gmail.com>
    >
    >


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