linux-kernel - [PATCH] ring-buffer: use atomic_[set|clear]

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Date:	Wed, 15 Oct 2014 09:41:40 -0400
From:	Patrick Palka <patrick@...cs.ath.cx>
To:	linux-kernel@...r.kernel.org
Cc:	Patrick Palka <patrick@...cs.ath.cx>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...hat.com>
Subject: [PATCH] ring-buffer: use atomic_[set|clear]_mask in place of a cmpxchg loop

Instead of open-coding the equivalent cmpxchg loop we can just use
atomic_set_mask and atomic_clear_mask to atomically OR or AND
the value in &buffer->record_disabled.

Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Ingo Molnar <mingo@...hat.com>
Signed-off-by: Patrick Palka <patrick@...cs.ath.cx>
---

NB: I have only tested this patch on x86_64 by booting with
CONFIG_RING_BUFFER_STARTUP_TEST=y.

 kernel/trace/ring_buffer.c | 16 ++--------------
 1 file changed, 2 insertions(+), 14 deletions(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 2d75c94..e15ce2a 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -3050,13 +3050,7 @@ EXPORT_SYMBOL_GPL(ring_buffer_record_enable);
  */
 void ring_buffer_record_off(struct ring_buffer *buffer)
 {
-	unsigned int rd;
-	unsigned int new_rd;
-
-	do {
-		rd = atomic_read(&buffer->record_disabled);
-		new_rd = rd | RB_BUFFER_OFF;
-	} while (atomic_cmpxchg(&buffer->record_disabled, rd, new_rd) != rd);
+	atomic_set_mask(RB_BUFFER_OFF, &buffer->record_disabled);
 }
 EXPORT_SYMBOL_GPL(ring_buffer_record_off);
 
@@ -3073,13 +3067,7 @@ EXPORT_SYMBOL_GPL(ring_buffer_record_off);
  */
 void ring_buffer_record_on(struct ring_buffer *buffer)
 {
-	unsigned int rd;
-	unsigned int new_rd;
-
-	do {
-		rd = atomic_read(&buffer->record_disabled);
-		new_rd = rd & ~RB_BUFFER_OFF;
-	} while (atomic_cmpxchg(&buffer->record_disabled, rd, new_rd) != rd);
+	atomic_clear_mask(RB_BUFFER_OFF, &buffer->record_disabled);
 }
 EXPORT_SYMBOL_GPL(ring_buffer_record_on);
 
-- 
2.1.2.443.g670a3c1

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