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 94EA4E7C4E7 for ; Wed, 4 Oct 2023 18:05:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S243797AbjJDSFm (ORCPT ); Wed, 4 Oct 2023 14:05:42 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46606 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S243799AbjJDSFl (ORCPT ); Wed, 4 Oct 2023 14:05:41 -0400 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7A89E9E for ; Wed, 4 Oct 2023 11:05:36 -0700 (PDT) Received: by smtp.kernel.org (Postfix) with ESMTPSA id B39BCC433C8; Wed, 4 Oct 2023 18:05:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1696442736; bh=skqfc3VETUbPS8f8EGvZRFuEDpouwRimtcyOX+dBsRM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=XbsdzuzR6Y1I+HsjAO8y9gR17nJgi1vnx+4qS8NXZTnOlCTCPVGwGRz80lyipTn6a 7zweiflW9YsNxZHfuCUoI1dv/O0vJU2T3dKcnGzfMxKCf4pu40gYMSg9bB6N1Z0zy7 jD0jAoBXVdFN83UYAIbacauBBEkp1hixePRqDIEk= 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 5.15 063/183] locking/seqlock: Do the lockdep annotation before locking in do_write_seqcount_begin_nested() Date: Wed, 4 Oct 2023 19:54:54 +0200 Message-ID: <20231004175206.520620226@linuxfoundation.org> X-Mailer: git-send-email 2.42.0 In-Reply-To: <20231004175203.943277832@linuxfoundation.org> References: <20231004175203.943277832@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 5.15-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 37ded6b8fee61..2c5d0102315d2 100644 --- a/include/linux/seqlock.h +++ b/include/linux/seqlock.h @@ -516,8 +516,8 @@ 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