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

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Message-ID: <20251109163559.4102849-3-chen.dylane@linux.dev>
Date: Mon, 10 Nov 2025 00:35:58 +0800
From: Tao Chen <chen.dylane@...ux.dev>
To: peterz@...radead.org,
	mingo@...hat.com,
	acme@...nel.org,
	namhyung@...nel.org,
	mark.rutland@....com,
	alexander.shishkin@...ux.intel.com,
	jolsa@...nel.org,
	irogers@...gle.com,
	adrian.hunter@...el.com,
	kan.liang@...ux.intel.com
Cc: linux-perf-users@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	bpf@...r.kernel.org,
	Tao Chen <chen.dylane@...ux.dev>,
	Yonghong Song <yonghong.song@...ux.dev>
Subject: [PATCH bpf-next v5 2/3] 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 <yonghong.song@...ux.dev>
Signed-off-by: Tao Chen <chen.dylane@...ux.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