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

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Date:	Tue, 31 Mar 2015 10:07:54 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Ingo Molnar <mingo@...nel.org>, Christoph Lameter <cl@...ux.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: [for-next][PATCH] ring-buffer: Remove duplicate use of '&' in
 recursive code

  git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git
for-next

Head SHA1: d631c8cceb1d1d06f372878935949d421585186b


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

----
 kernel/trace/ring_buffer.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)
---------------------------
commit d631c8cceb1d1d06f372878935949d421585186b
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.
    
    And Christoph even mentioned that it can be further compacted to
    just a single line:
    
      __this_cpu_and(current_context, __this_cpu_read(current_context) - 1);
    
    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..0315d43176d8 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -2703,10 +2703,7 @@ static __always_inline int trace_recursive_lock(void)
 
 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_and(current_context, __this_cpu_read(current_context) - 1);
 }
 
 #else
--
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