[PATCH][3.7] ring-buffer: Check for uninitialized cpu buffer before resizing

[Steven Rostedt <rostedt@goodmis.org>]

Ingo,

Please pull the latest tip/perf/urgent tree, which can be found at:

  git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git
tip/perf/urgent

Head SHA1: 8e49f418c9632790bf456634742d34d97120a784


Vaibhav Nagarnaik (1):
      ring-buffer: Check for uninitialized cpu buffer before resizing

----
 kernel/trace/ring_buffer.c |    4 ++++
 1 file changed, 4 insertions(+)
---------------------------
commit 8e49f418c9632790bf456634742d34d97120a784
Author: Vaibhav Nagarnaik <vnagarnaik@google.com>
Date:   Wed Oct 10 16:40:27 2012 -0700

    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@google.com
    
    Cc: stable@vger.kernel.org # 3.5+
    Signed-off-by: Vaibhav Nagarnaik <vnagarnaik@google.com>
    Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

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)