From nobody Tue Sep 9 21:32:23 2025 Received: from szxga04-in.huawei.com (szxga04-in.huawei.com [45.249.212.190]) (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 18F72EACD; Mon, 8 Sep 2025 02:20:06 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.249.212.190 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757298010; cv=none; b=flUzA1jdfPUs4u6n24q4Slq9v4end/IpVzCRZzQfJI/TTejmIlnuK/zBwp3mxYVfBmeMEScxqEzous0J0rq9/RoZps1xAPMS/nYyvMfP8wXfifCwub5uW8njO7QiU/8x7jmttkomQvj/HxRMW1cOIn34yG3sbST8UU9XEK/7y8Q= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757298010; c=relaxed/simple; bh=KRSfORJrFl0gP3PLxItagIn9DLD7WCyexIdVlQZwDww=; h=From:To:CC:Subject:Date:Message-ID:MIME-Version:Content-Type; b=qYHq4AlPgUB2xBcrSIbjNWainUiBE3TE75wjA/+EMCZOAehTPmN2j6d6/xLdCjqrNSgsHe57TE5IybSEr1sqLInD1YiSeNI/gPzCy2RFgxURXNLSZj36scmkFQhNt2h/s5kKYG+ntPnKMjrmcU2imGcLmZ2PZ/tH8SR4Bxy5yb0= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com; spf=pass smtp.mailfrom=huawei.com; arc=none smtp.client-ip=45.249.212.190 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huawei.com Received: from mail.maildlp.com (unknown [172.19.88.214]) by szxga04-in.huawei.com (SkyGuard) with ESMTP id 4cKrDY4Rl4z2TT3C; Mon, 8 Sep 2025 10:16:45 +0800 (CST) Received: from dggemv705-chm.china.huawei.com (unknown [10.3.19.32]) by mail.maildlp.com (Postfix) with ESMTPS id 96C401A016C; Mon, 8 Sep 2025 10:19:58 +0800 (CST) Received: from kwepemn200010.china.huawei.com (7.202.194.133) by dggemv705-chm.china.huawei.com (10.3.19.32) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.11; Mon, 8 Sep 2025 10:19:58 +0800 Received: from huawei.com (10.44.142.84) by kwepemn200010.china.huawei.com (7.202.194.133) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.11; Mon, 8 Sep 2025 10:19:57 +0800 From: Qi Xi To: , , , , , , , CC: Subject: [PATCH v2] once: fix race by moving DO_ONCE to separate section Date: Mon, 8 Sep 2025 10:10:36 +0800 Message-ID: <20250908021036.1971956-1-xiqi2@huawei.com> X-Mailer: git-send-email 2.33.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-ClientProxiedBy: kwepems200001.china.huawei.com (7.221.188.67) To kwepemn200010.china.huawei.com (7.202.194.133) Content-Type: text/plain; charset="utf-8" The commit c2c60ea37e5b ("once: use __section(".data.once")") moved DO_ONCE's ___done variable to .data.once section, which conflicts with DO_ONCE_LITE() that also uses the same section. This creates a race condition when clear_warn_once is used: Thread 1 (DO_ONCE) Thread 2 (DO_ONCE) __do_once_start read ___done (false) acquire once_lock execute func __do_once_done write ___done (true) __do_once_start release once_lock // Thread 3 clear_warn_once reset ___done read ___done (false) acquire once_lock execute func schedule once_work __do_once_done once_deferred: OK write ___done (true) static_branch_disable release once_lock schedule once_work once_deferred: BUG_ON(!static_key_enabled) DO_ONCE_LITE() in once_lite.h is used by WARN_ON_ONCE() and other warning macros. Keep its ___done flag in the .data..once section and allow resetting by clear_warn_once, as originally intended. In contrast, DO_ONCE() is used for functions like get_random_once() and relies on its ___done flag for internal synchronization. We should not reset DO_ONCE() by clear_warn_once. Fix it by isolating DO_ONCE's ___done into a separate .data..do_once sectio= n, shielding it from clear_warn_once. Fixes: c2c60ea37e5b ("once: use __section(".data.once")") Signed-off-by: Qi Xi --- include/asm-generic/vmlinux.lds.h | 1 + include/linux/once.h | 2 +- 2 files changed, 2 insertions(+), 1 deletion(-) diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinu= x.lds.h index ae2d2359b79e..8efbe8c4874e 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -361,6 +361,7 @@ defined(CONFIG_AUTOFDO_CLANG) || defined(CONFIG_PROPELL= ER_CLANG) __start_once =3D .; \ *(.data..once) \ __end_once =3D .; \ + *(.data..do_once) \ STRUCT_ALIGN(); \ *(__tracepoints) \ /* implement dynamic printk debug */ \ diff --git a/include/linux/once.h b/include/linux/once.h index 30346fcdc799..261a7a4977dd 100644 --- a/include/linux/once.h +++ b/include/linux/once.h @@ -46,7 +46,7 @@ void __do_once_sleepable_done(bool *done, struct static_k= ey_true *once_key, #define DO_ONCE(func, ...) \ ({ \ bool ___ret =3D false; \ - static bool __section(".data..once") ___done =3D false; \ + static bool __section(".data..do_once") ___done =3D false; \ static DEFINE_STATIC_KEY_TRUE(___once_key); \ if (static_branch_unlikely(&___once_key)) { \ unsigned long ___flags; \ --=20 2.33.0