ring_buffer: Fix warning while ignoring cmpxchg return value

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, because we don't need here to handle
the fail case of cmpxchg, it's fine if an interrupt already did the
job.

Changed from V1:
  Add a comment(which is written by Steven) for it.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index e648ba4f70e0c15c528b8767b6b41f754450e7ab..51633d74a21eaae376771390f0b562455552e21a 100644 (file)
--- 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.