tracing: Add checks if tr->buffer is NULL in tracing_reset{_online_cpus}

max_tr->buffer could be NULL in the tracing_reset{_online_cpus}. In this
case, a NULL pointer dereference happens, so we should return immediately
from these functions.

Note, the current code does not call tracing_reset*() with max_tr when
its buffer is NULL, but future code will. This patch is needed to prevent
the future code from crashing.

Link: http://lkml.kernel.org/r/20121219070234.31200.93863.stgit@liselsia

Signed-off-by: Hiraku Toyooka <hiraku.toyooka.gu@hitachi.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 6 insertions, 0 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index f8b7c626f3fd..72b171b90e55 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -922,6 +922,9 @@ void tracing_reset(struct trace_array *tr, int cpu)
 {
         struct ring_buffer *buffer = tr->buffer;
 
+        if (!buffer)
+                return;
+
         ring_buffer_record_disable(buffer);
 
         /* Make sure all commits have finished */
@@ -936,6 +939,9 @@ void tracing_reset_online_cpus(struct trace_array *tr)
         struct ring_buffer *buffer = tr->buffer;
         int cpu;
 
+        if (!buffer)
+                return;
+
         ring_buffer_record_disable(buffer);
 
         /* Make sure all commits have finished */