Patch "ftrace: Check for null ret_stack on profile function graph entry function" has been added to the 4.12-stable tree

[<gregkh@linuxfoundation.org>]

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 4.12-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-4.12 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From a8f0f9e49956a74718874b800251455680085600 Mon Sep 17 00:00:00 2001
From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>
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@goodmis.org>

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@gmail.com
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 kernel/trace/ftrace.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -878,6 +878,10 @@ 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@goodmis.org are

queue-4.12/tracing-missing-error-code-in-tracer_alloc_buffers.patch
queue-4.12/ring-buffer-have-ring_buffer_alloc_read_page-return-error-on-offline-cpu.patch
queue-4.12/ftrace-check-for-null-ret_stack-on-profile-function-graph-entry-function.patch
queue-4.12/tracing-fix-freeing-of-filter-in-create_filter-when-set_str-is-false.patch
queue-4.12/tracing-call-clear_boot_tracer-at-lateinit_sync.patch
queue-4.12/tracing-fix-kmemleak-in-tracing_map_array_free.patch