linux-kernel - [PATCH] ring-buffer: Remove duplicate use of '&' in recursive code

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Message-ID: <20150327175033.66ca3553@gandalf.local.home>
Date:	Fri, 27 Mar 2015 17:50:33 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Christoph Lameter <cl@...ux.com>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	stable@...r.kernel.org,
	Uwe Kleine-Koenig <u.kleine-koenig@...gutronix.de>
Subject: [PATCH] ring-buffer: Remove duplicate use of '&' in recursive code


Steven Rostedt (Red Hat) (1):
      ring-buffer: Remove duplicate use of '&' in recursive code

----
 kernel/trace/ring_buffer.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)
---------------------------
commit 7eb867195b9f3990da60738b1f26d0a71f37f77f
Author: Steven Rostedt (Red Hat) <rostedt@...dmis.org>
Date:   Fri Mar 27 17:39:49 2015 -0400

    ring-buffer: Remove duplicate use of '&' in recursive code
    
    A clean up of the recursive protection code changed
    
      val = this_cpu_read(current_context);
      val--;
      val &= this_cpu_read(current_context);
    
    to
    
      val = this_cpu_read(current_context);
      val &= val & (val - 1);
    
    Which has a duplicate use of '&' as the above is the same as
    
      val = val & (val - 1);
    
    Actually, it would be best to remove that line altogether and
    just add it to where it is used.
    
    Link: http://lkml.kernel.org/alpine.DEB.2.11.1503271423580.23114@gentwo.org
    
    Suggested-by: Christoph Lameter <cl@...ux.com>
    Signed-off-by: Steven Rostedt <rostedt@...dmis.org>

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 922048a0f7ea..93caf56567cb 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -2705,8 +2705,7 @@ static __always_inline void trace_recursive_unlock(void)
 {
 	unsigned int val = __this_cpu_read(current_context);
 
-	val &= val & (val - 1);
-	__this_cpu_write(current_context, val);
+	__this_cpu_write(current_context, val & (val - 1));
 }
 
 #else
--
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