linux-kernel - [016/116] ring-buffer: Move disabled check into preempt disable section

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Date:	Tue, 30 Mar 2010 15:54:54 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Greg Kroah-Hartman <gregkh@...e.de>
Subject: [016/116] ring-buffer: Move disabled check into preempt disable section

2.6.32-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Lai Jiangshan <laijs@...fujitsu.com>

commit 52fbe9cde7fdb5c6fac196d7ebd2d92d05ef3cd4 upstream.

The ring buffer resizing and resetting relies on a schedule RCU
action. The buffers are disabled, a synchronize_sched() is called
and then the resize or reset takes place.

But this only works if the disabling of the buffers are within the
preempt disabled section, otherwise a window exists that the buffers
can be written to while a reset or resize takes place.

Reported-by: Li Zefan <lizf@...fujitsu.com>
Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
LKML-Reference: <4B949E43.2010906@...fujitsu.com>
Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 kernel/trace/ring_buffer.c |   12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -2237,12 +2237,12 @@ ring_buffer_lock_reserve(struct ring_buf
 	if (ring_buffer_flags != RB_BUFFERS_ON)
 		return NULL;
 
-	if (atomic_read(&buffer->record_disabled))
-		return NULL;
-
 	/* If we are tracing schedule, we don't want to recurse */
 	resched = ftrace_preempt_disable();
 
+	if (atomic_read(&buffer->record_disabled))
+		goto out_nocheck;
+
 	if (trace_recursive_lock())
 		goto out_nocheck;
 
@@ -2474,11 +2474,11 @@ int ring_buffer_write(struct ring_buffer
 	if (ring_buffer_flags != RB_BUFFERS_ON)
 		return -EBUSY;
 
-	if (atomic_read(&buffer->record_disabled))
-		return -EBUSY;
-
 	resched = ftrace_preempt_disable();
 
+	if (atomic_read(&buffer->record_disabled))
+		goto out;
+
 	cpu = raw_smp_processor_id();
 
 	if (!cpumask_test_cpu(cpu, buffer->cpumask))


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