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

[tip-bot for Vaibhav Nagarnaik]

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,
 
 		put_online_cpus();
 	} 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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