From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id A3DDFE95A8E for ; Mon, 9 Oct 2023 13:38:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1377243AbjJINii (ORCPT ); Mon, 9 Oct 2023 09:38:38 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51056 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1377292AbjJINia (ORCPT ); Mon, 9 Oct 2023 09:38:30 -0400 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B12EF107 for ; Mon, 9 Oct 2023 06:38:26 -0700 (PDT) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2F529C433C8; Mon, 9 Oct 2023 13:38:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1696858706; bh=EgJ5HWX1m61vhwxKknitBJAij2SE8LDY+IOeYnlzGbA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=m6vCRy3cz1/PWyjRD7zJpUsBklhDq9z7VoNAmVsdWVDMwaTL9Fp/MtfTx9VROMEP0 ohV99DFIHyok1PXMM4zCkxYNfp+9Diw8JPO+zx8qtn7a3GgvIlOGow+0/9V+lHpjuC mnGI0Hki4wB3gX8QUGhZ8f4qYwM6+ag4CogC74NM= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Tetsuo Handa , Sebastian Andrzej Siewior , Ingo Molnar , Sasha Levin Subject: [PATCH 5.10 057/226] locking/seqlock: Do the lockdep annotation before locking in do_write_seqcount_begin_nested() Date: Mon, 9 Oct 2023 15:00:18 +0200 Message-ID: <20231009130128.278968140@linuxfoundation.org> X-Mailer: git-send-email 2.42.0 In-Reply-To: <20231009130126.697995596@linuxfoundation.org> References: <20231009130126.697995596@linuxfoundation.org> User-Agent: quilt/0.67 X-stable: review X-Patchwork-Hint: ignore MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org 5.10-stable review patch. If anyone has any objections, please let me know. ------------------ From: Sebastian Andrzej Siewior [ Upstream commit 41b43b6c6e30a832c790b010a06772e793bca193 ] It was brought up by Tetsuo that the following sequence: write_seqlock_irqsave() printk_deferred_enter() could lead to a deadlock if the lockdep annotation within write_seqlock_irqsave() triggers. The problem is that the sequence counter is incremented before the lockdep annotation is performed. The lockdep splat would then attempt to invoke printk() but the reader side, of the same seqcount, could have a tty_port::lock acquired waiting for the sequence number to become even again. The other lockdep annotations come before the actual locking because "we want to see the locking error before it happens". There is no reason why seqcount should be different here. Do the lockdep annotation first then perform the locking operation (the sequence increment). Fixes: 1ca7d67cf5d5a ("seqcount: Add lockdep functionality to seqcount/seqlock structures") Reported-by: Tetsuo Handa Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Ingo Molnar Link: https://lore.kernel.org/r/20230920104627._DTHgPyA@linutronix.de Closes: https://lore.kernel.org/20230621130641.-5iueY1I@linutronix.de Signed-off-by: Sasha Levin --- include/linux/seqlock.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h index 008fa88ad58e7..0928a60b8f825 100644 --- a/include/linux/seqlock.h +++ b/include/linux/seqlock.h @@ -511,8 +511,8 @@ do { \ static inline void do_write_seqcount_begin_nested(seqcount_t *s, int subclass) { - do_raw_write_seqcount_begin(s); seqcount_acquire(&s->dep_map, subclass, 0, _RET_IP_); + do_raw_write_seqcount_begin(s); } /** -- 2.40.1