From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>
Date: Thu, 17 Aug 2017 16:37:25 -0400
Subject: [PATCH] ftrace: Check for null ret_stack on profile function graph
entry function
References: bnc#1060662
Patch-mainline: v4.12.10
Git-commit: a8f0f9e49956a74718874b800251455680085600
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>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
kernel/trace/ftrace.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 28e980d2851b..a2bbce575e88 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -878,6 +878,10 @@ static int profile_graph_entry(struct ftrace_graph_ent *trace)
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;
--
2.14.2