[PATCH bpf-next v5 2/3] perf: Add atomic operation in get_recursion_context

Tao Chen
2025-11-09T16:37:01Z

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 <yonghong.song@linux.dev>
Signed-off-by: Tao Chen <chen.dylane@linux.dev>
---
kernel/events/internal.h | 5 +----
1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/kernel/events/internal.h b/kernel/events/internal.h
index d9cc5708309..684bde972ba 100644
--- a/kernel/events/internal.h
+++ b/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;
}

--
2.48.1