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 <[email protected]>

Cc Steven Rostedt <[email protected]>

Cc Andi Kleen <[email protected]>

---
 arch/x86/kernel/ftrace.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

arch/x86/kernel/ftrace.c +1 -0

index fe83273..db25236 100644
@@ -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;

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 <[email protected]>

Cc Steven Rostedt <[email protected]>