tracing/function-return-tracer: add a barrier to ensure return stack index is incremented in memory

Impact: fix possible race condition in ftrace function return tracer

This fixes a possible race condition if index incrementation
is not immediately flushed in memory.

Thanks for Andi Kleen and Steven Rostedt for pointing out this issue
and give me this solution.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 1 insertions, 0 deletions

diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index 762222ad1387..d98b5a8ecf4c 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -56,6 +56,7 @@ static int push_return_trace(unsigned long ret, unsigned long long time,
                 return -EBUSY;
 
         index = ++ti->curr_ret_stack;
+        barrier();
         ti->ret_stack[index].ret = ret;
         ti->ret_stack[index].func = func;
         ti->ret_stack[index].calltime = time;