From: Steven Rostedt (VMware) Date: Thu, 17 Aug 2017 20:37:25 +0000 (-0400) Subject: ftrace: Check for null ret_stack on profile function graph entry function X-Git-Tag: C0P2-H0.0--20200415~7668 X-Git-Url: https://git.somdevices.com/?a=commitdiff_plain;h=741397d16a3d65e1629e9be75f5d64687d767664;p=linux.git ftrace: Check for null ret_stack on profile function graph entry function 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) Signed-off-by: Greg Kroah-Hartman --- diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c index 4f7ea8446bb5..6e432ed7d0fe 100644 --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -876,6 +876,10 @@ 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;