This is a note to let you know that I've just added the patch titled ftrace: Check for null ret_stack on profile function graph entry function to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: ftrace-check-for-null-ret_stack-on-profile-function-graph-entry-function.patch and it can be found in the queue-4.9 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From a8f0f9e49956a74718874b800251455680085600 Mon Sep 17 00:00:00 2001 From: "Steven Rostedt (VMware)" <rostedt@xxxxxxxxxxx> Date: Thu, 17 Aug 2017 16:37:25 -0400 Subject: ftrace: Check for null ret_stack on profile function graph entry function From: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx> 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: lilydjwg@xxxxxxxxx Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- 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; Patches currently in stable-queue which might be from rostedt@xxxxxxxxxxx are queue-4.9/ftrace-check-for-null-ret_stack-on-profile-function-graph-entry-function.patch queue-4.9/tracing-fix-freeing-of-filter-in-create_filter-when-set_str-is-false.patch queue-4.9/tracing-call-clear_boot_tracer-at-lateinit_sync.patch queue-4.9/tracing-fix-kmemleak-in-tracing_map_array_free.patch