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From: Greg KH on 30 Mar 2010 19:50
2.6.33-stable review patch. If anyone has any objections, please let us know.

------------------

From: Steven Rostedt <srostedt(a)redhat.com>

commit ea14eb714041d40fcc5180b5a586034503650149 upstream.

If the graph tracer is active, and a task is forked but the allocating of
the processes graph stack fails, it can cause crash later on.

This is due to the temporary stack being NULL, but the curr_ret_stack
variable is copied from the parent. If it is not -1, then in
ftrace_graph_probe_sched_switch() the following:

for (index = next->curr_ret_stack; index >= 0; index--)
next->ret_stack[index].calltime += timestamp;

Will cause a kernel OOPS.

Found with Li Zefan's ftrace_stress_test.

Signed-off-by: Steven Rostedt <rostedt(a)goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh(a)suse.de>

---
kernel/trace/ftrace.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -3364,6 +3364,7 @@ void ftrace_graph_init_task(struct task_
{
/* Make sure we do not use the parent ret_stack */
t->ret_stack = NULL;
+ t->curr_ret_stack = -1;

if (ftrace_graph_active) {
struct ftrace_ret_stack *ret_stack;
@@ -3373,7 +3374,6 @@ void ftrace_graph_init_task(struct task_
GFP_KERNEL);
if (!ret_stack)
return;
- t->curr_ret_stack = -1;
atomic_set(&t->tracing_graph_pause, 0);
atomic_set(&t->trace_overrun, 0);
t->ftrace_timestamp = 0;


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