[tip:perf/urgent] ring-buffer: Check for uninitialized cpu buffer before resizing

From: tip-bot for Vaibhav Nagarnaik
Date: Sun Oct 21 2012 - 14:37:41 EST

Commit-ID: 8e49f418c9632790bf456634742d34d97120a784
Gitweb: http://git.kernel.org/tip/8e49f418c9632790bf456634742d34d97120a784
Author: Vaibhav Nagarnaik <vnagarnaik@xxxxxxxxxx>
AuthorDate: Wed, 10 Oct 2012 16:40:27 -0700
Committer: Steven Rostedt <rostedt@xxxxxxxxxxx>
CommitDate: Thu, 11 Oct 2012 12:21:48 -0400

ring-buffer: Check for uninitialized cpu buffer before resizing

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@xxxxxxxxxx

Cc: stable@xxxxxxxxxxxxxxx # 3.5+
Signed-off-by: Vaibhav Nagarnaik <vnagarnaik@xxxxxxxxxx>
Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
kernel/trace/ring_buffer.c | 4 ++++
1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index b32ed0e..b979426 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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