From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from m16.mail.163.com (m16.mail.163.com [220.197.31.5]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2657E3FBB7D for ; Tue, 13 Oct 2026 14:27:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=220.197.31.5 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791901662; cv=none; b=lgYCsuyfBVZ3Ryxk4TUBVZrTtJVcbSXNnq3Z1Evrh/QS4TS859t5hDIG8onLlvl2c8G6JAACo0fmI7VCbC6C5Yq0/dTCBKgGS3aO1OaYKpB4pHiBNGNccAV0DFHYzYpAR8pAgBp+UY/67pJBTVJc5W013Oi7p/RF16pzvHgMslk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791901662; c=relaxed/simple; bh=NZKnBMsTlEv5VIQbgRx+b8+0ULAauvjEqoSq3YJNCkM=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=eNn1GA6uIll0hKuU7vwGJT8kc+ywPI5fYTcNNYeKu2/3KyEtEglrieY9YgNzIdhHGyvjKLtHnWu6z+4zu/Mj57w09xHVUfxp0Z5cTJyTvTj4r9DoZhJp3HRkcpgFy6IG/r9lU6mmCMmIsjMByc2nrVBVt4CA6WjRJpzOCEXdGkc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=163.com; spf=pass smtp.mailfrom=163.com; dkim=pass (1024-bit key) header.d=163.com header.i=@163.com header.b=emB06pHt; arc=none smtp.client-ip=220.197.31.5 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=163.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=163.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=163.com header.i=@163.com header.b="emB06pHt" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=163.com; s=s110527; h=From:To:Subject:Date:Message-ID:MIME-Version; bh=iX DAwEzI6YClfsZwoWfAR4r7aRqTD5xFqxKyONFlpj4=; b=emB06pHtLC9JvSScmY Vkw55ndjFyBWvk5hm61jR5lEewnTIw5Tdi8w8DxbFTH5Y5kvmSbauazMS1L8DSv1 2IHWJMWlhm8wFP6s8IMjLOjRvkqGs/kAa0J9G1L65K9KEqdr87cpjv+T469WmaeI vpON0ArvA8cE4dTfmif6C1UwM= Received: from localhost (unknown []) by gzsmtp3 (Coremail) with SMTP id PigvCgD3f+SJP85q22CyEQ--.43028S2; Tue, 13 Oct 2026 22:26:18 +0800 (CST) From: Hui Su To: mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org Cc: dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, kprateek.nayak@amd.com, linux-kernel@vger.kernel.org, sh_def@163.com Subject: [PATCH] sched/loadavg: Use READ_ONCE/WRITE_ONCE for calc_load_idx Date: Tue, 13 Oct 2026 23:25:52 +0900 Message-ID: <20261013142552.262520-1-sh_def@163.com> X-Mailer: git-send-email 2.55.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-CM-TRANSID:PigvCgD3f+SJP85q22CyEQ--.43028S2 X-Coremail-Antispam: 1Uf129KBjvJXoW7uFykWrW7Jr48Aw4fWF18AFb_yoW8ZF45pF 92yFyUGr48XF1rZa97ua4UCrn8Wrn7CF43JF1vyrs2vF4DKF1DKF1IgF1a9FyYgrn3A3Wj qrWjvry7Kw4q9w7anT9S1TB71UUUUU7qnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDUYxBIdaVFxhVjvjDU0xZFpf9x0pRiYFJUUUUU= X-CM-SenderInfo: xvkbvvri6rljoofrz/xtbC6QpAn2rOP4rjvAAA3y The NO_HZ fold path reads calc_load_idx locklessly from calc_load_write_idx(), while calc_global_nohz() updates it from the jiffies_lock-serialized global load path. Commit caeb5882979b ("sched/loadavg: Use {READ,WRITE}_ONCE() for sample window") marked the lockless accesses to calc_load_update. calc_load_idx participates in the same cross-CPU protocol, ordered by the existing smp_wmb()/smp_rmb() pair, but its accesses remain plain C accesses. Mark the lockless read and publisher access with READ_ONCE() and WRITE_ONCE(). KCSAN otherwise observes the concurrent access: BUG: KCSAN: data-race in calc_global_load / calc_load_nohz_fold write by interrupt on cpu 3: calc_global_load+0x392/0x420 tick_do_update_jiffies64+0x171/0x1e0 read by task 0 on cpu 5: calc_load_nohz_fold+0x7a/0x110 calc_load_nohz_start+0x26/0x30 value changed: 0x00000033 -> 0x00000034 Keep the existing memory ordering and writer serialization unchanged. calc_load_read_idx() is only used from the jiffies_lock-serialized global load path and does not need an accessor. Fixes: 5167e8d5417b ("sched/nohz: Rewrite and fix load-avg computation -- again") Signed-off-by: Hui Su --- kernel/sched/loadavg.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/sched/loadavg.c b/kernel/sched/loadavg.c index b601e0243d0e..f87059e0e251 100644 --- a/kernel/sched/loadavg.c +++ b/kernel/sched/loadavg.c @@ -209,7 +209,7 @@ static int calc_load_idx; static inline int calc_load_write_idx(void) { - int idx = calc_load_idx; + int idx = READ_ONCE(calc_load_idx); /* * See calc_global_nohz(), if we observe the new index, we also @@ -333,7 +333,7 @@ static void calc_global_nohz(void) * index, this avoids a double flip messing things up. */ smp_wmb(); - calc_load_idx++; + WRITE_ONCE(calc_load_idx, READ_ONCE(calc_load_idx) + 1); } #else /* !CONFIG_NO_HZ_COMMON: */ -- 2.55.0