function-graph: always initialize task ret_stack
On creating a new task while running the function graph tracer, if
we fail to allocate the ret_stack, and then fail the fork, the
code will free the parent ret_stack. This is because the child
duplicated the parent and currently points to the parent's ret_stack.
This patch always initializes the task's ret_stack to NULL.
[ Impact: prevent crash of parent on low memory during fork ]
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 1664d3f..bb081f3 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -2738,6 +2738,9 @@
/* Allocate a return stack for newly created task */
void ftrace_graph_init_task(struct task_struct *t)
{
+ /* Make sure we do not use the parent ret_stack */
+ t->ret_stack = NULL;
+
if (atomic_read(&ftrace_graph_active)) {
struct ftrace_ret_stack *ret_stack;
@@ -2753,8 +2756,7 @@
/* make curr_ret_stack visable before we add the ret_stack */
smp_wmb();
t->ret_stack = ret_stack;
- } else
- t->ret_stack = NULL;
+ }
}
void ftrace_graph_exit_task(struct task_struct *t)
