4.9-stable review patch. If anyone has any objections, please let me know.
------------------ From: Steven Rostedt (VMware) <[email protected]> commit a8f0f9e49956a74718874b800251455680085600 upstream. There's a small race when function graph shutsdown and the calling of the registered function graph entry callback. The callback must not reference the task's ret_stack without first checking that it is not NULL. Note, when a ret_stack is allocated for a task, it stays allocated until the task exits. The problem here, is that function_graph is shutdown, and a new task was created, which doesn't have its ret_stack allocated. But since some of the functions are still being traced, the callbacks can still be called. The normal function_graph code handles this, but starting with commit 8861dd303c ("ftrace: Access ret_stack->subtime only in the function profiler") the profiler code references the ret_stack on function entry, but doesn't check if it is NULL first. Link: https://bugzilla.kernel.org/show_bug.cgi?id=196611 Fixes: 8861dd303c ("ftrace: Access ret_stack->subtime only in the function profiler") Reported-by: [email protected] Signed-off-by: Steven Rostedt (VMware) <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]> --- kernel/trace/ftrace.c | 4 ++++ 1 file changed, 4 insertions(+) --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -876,6 +876,10 @@ static int profile_graph_entry(struct ft function_profile_call(trace->func, 0, NULL, NULL); + /* If function graph is shutting down, ret_stack can be NULL */ + if (!current->ret_stack) + return 0; + if (index >= 0 && index < FTRACE_RETFUNC_DEPTH) current->ret_stack[index].subtime = 0;
