perf: Add atomic operation in get_recursion_context

From BPF side, preemption usually is enabled. Yonghong said, it is
possible that both tasks (at process level) may reach right before
"recursion[rctx]++;". In such cases, both tasks will be able to get
buffer and this is not right.

Signed-off-by: Yonghong Song <[email protected]>
Signed-off-by: Tao Chen <[email protected]>

Author: Tao Chen

kernel/events/internal.h

@@ -214,12 +214,9 @@ static inline int get_recursion_context(u8 *recursion)
 {
 	unsigned char rctx = interrupt_context_level();
 
-	if (recursion[rctx])
+	if (cmpxchg(&recursion[rctx], 0, 1) != 0)
 		return -1;
 
-	recursion[rctx]++;
-	barrier();
-
 	return rctx;
 }