[ 3.5.yuz extended stable ] Patch "ring-buffer: Check for uninitialized cpu buffer before" has been added to staging queue

Herton Ronaldo Krzesinski herton.krzesinski at canonical.com
Thu Nov 22 04:45:27 UTC 2012

This is a note to let you know that I have just added a patch titled

    ring-buffer: Check for uninitialized cpu buffer before

to the linux-3.5.y-queue branch of the 3.5.yuz extended stable tree 
which can be found at:


If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.yuz tree, see



>From 6e3a3172e7808e9a0f43ef0d0f2383a085022546 Mon Sep 17 00:00:00 2001
From: Vaibhav Nagarnaik <vnagarnaik at google.com>
Date: Wed, 10 Oct 2012 16:40:27 -0700
Subject: [PATCH] ring-buffer: Check for uninitialized cpu buffer before

commit 8e49f418c9632790bf456634742d34d97120a784 upstream.

With a system where, num_present_cpus < num_possible_cpus, even if all
CPUs are online, non-present CPUs don't have per_cpu buffers allocated.
If per_cpu/<cpu>/buffer_size_kb is modified for such a CPU, it can cause
a panic due to NULL dereference in ring_buffer_resize().

To fix this, resize operation is allowed only if the per-cpu buffer has
been initialized.

Link: http://lkml.kernel.org/r/1349912427-6486-1-git-send-email-vnagarnaik@google.com

Signed-off-by: Vaibhav Nagarnaik <vnagarnaik at google.com>
Signed-off-by: Steven Rostedt <rostedt at goodmis.org>
Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesinski at canonical.com>
 kernel/trace/ring_buffer.c |    4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index f765465..db6dff1 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -1567,6 +1567,10 @@ int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size,

 	} else {
+		/* Make sure this CPU has been intitialized */
+		if (!cpumask_test_cpu(cpu_id, buffer->cpumask))
+			goto out;
 		cpu_buffer = buffer->buffers[cpu_id];

 		if (nr_pages == cpu_buffer->nr_pages)

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