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 99913E7C4E9 for ; Wed, 4 Oct 2023 18:13:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S243928AbjJDSNq (ORCPT ); Wed, 4 Oct 2023 14:13:46 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41886 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S243752AbjJDSNp (ORCPT ); Wed, 4 Oct 2023 14:13:45 -0400 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A5682C1 for ; Wed, 4 Oct 2023 11:13:42 -0700 (PDT) Received: by smtp.kernel.org (Postfix) with ESMTPSA id D3674C433C8; Wed, 4 Oct 2023 18:13:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1696443222; bh=heSel1K3MXLrWOifxDd12lcx6fbJdCUClwsOzOxJyqA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=1sBwck/njPfzF2It6MllMxRFuC3JF1441C5qBkVbk3LGZLji0PA/gVgLQCQS0Vydv XI906o7B9DfV97Wcw9uqBdHoGj3JQSn9DDeDfkFWKw2ZSx4PbP0e5l3yWdrhYFK3wt mZMRHbsvWmrzcNtlduZJQofb+z+xcyxcwOPjIo7o= 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 6.1 080/259] locking/seqlock: Do the lockdep annotation before locking in do_write_seqcount_begin_nested() Date: Wed, 4 Oct 2023 19:54:13 +0200 Message-ID: <20231004175221.043937326@linuxfoundation.org> X-Mailer: git-send-email 2.42.0 In-Reply-To: <20231004175217.404851126@linuxfoundation.org> References: <20231004175217.404851126@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 6.1-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 3926e90279477..d778af83c8f36 100644 --- a/include/linux/seqlock.h +++ b/include/linux/seqlock.h @@ -512,8 +512,8 @@ 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