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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id A87CFEB64DA for ; Mon, 26 Jun 2023 12:56:26 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 09EBF8D0002; Mon, 26 Jun 2023 08:56:26 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 04E0A8D0001; Mon, 26 Jun 2023 08:56:25 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id EA5E38D0002; Mon, 26 Jun 2023 08:56:25 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id DA3ED8D0001 for ; Mon, 26 Jun 2023 08:56:25 -0400 (EDT) Received: from smtpin22.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay05.hostedemail.com (Postfix) with ESMTP id 7198F40693 for ; Mon, 26 Jun 2023 12:56:25 +0000 (UTC) X-FDA: 80944897530.22.B4BAE38 Received: from outbound-smtp25.blacknight.com (outbound-smtp25.blacknight.com [81.17.249.193]) by imf05.hostedemail.com (Postfix) with ESMTP id 30EA3100002 for ; Mon, 26 Jun 2023 12:56:22 +0000 (UTC) Authentication-Results: imf05.hostedemail.com; dkim=none; dmarc=none; spf=pass (imf05.hostedemail.com: domain of mgorman@techsingularity.net designates 81.17.249.193 as permitted sender) smtp.mailfrom=mgorman@techsingularity.net ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1687784183; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=2M8s+AXPxv/gB+GT8A7is8erJy7g4n9MFs2gGfoPyhg=; b=AOHXoh8/uy+YNxdQKl25AZ93GlFG+PqR0VMpgi3zv77n5nnTrfPB62+ZieyXvcjXWjXTGD gYjbL3RopPbniwxjh9NMJBoxagg487lbFiZiRX+X1QNPkHbNHMJbDz7pjEtxZ0IZRN1YCA Dhp8dhcgLBqIU4XXa+yEMMMLe0h6DEg= ARC-Authentication-Results: i=1; imf05.hostedemail.com; dkim=none; dmarc=none; spf=pass (imf05.hostedemail.com: domain of mgorman@techsingularity.net designates 81.17.249.193 as permitted sender) smtp.mailfrom=mgorman@techsingularity.net ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1687784183; a=rsa-sha256; cv=none; b=fs3e1f0640QOhzPLX52S/32QfxRYUdj8lfrlmeQWl49u2S6I/hGxSJ5Hk/d1ni3h/oBBQV hv8VOieNfQM8uDy2DZe57CXVoxxoVx+AQB9L75zSMTppjTffEp4F1dOq+bypfaC/QIGCTF uC+CCupnVPlbQgbaKFfZ1Ab738J5uXY= Received: from mail.blacknight.com (pemlinmail03.blacknight.ie [81.17.254.16]) by outbound-smtp25.blacknight.com (Postfix) with ESMTPS id 32661CAD6C for ; Mon, 26 Jun 2023 13:56:21 +0100 (IST) Received: (qmail 26177 invoked from network); 26 Jun 2023 12:56:21 -0000 Received: from unknown (HELO techsingularity.net) (mgorman@techsingularity.net@[84.203.21.103]) by 81.17.254.9 with ESMTPSA (AES256-SHA encrypted, authenticated); 26 Jun 2023 12:56:20 -0000 Date: Mon, 26 Jun 2023 13:56:18 +0100 From: Mel Gorman To: Sebastian Andrzej Siewior Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, "Luis Claudio R. Goncalves" , Andrew Morton , Boqun Feng , Ingo Molnar , John Ogness , Michal Hocko , Peter Zijlstra , Petr Mladek , Tetsuo Handa , Thomas Gleixner , Waiman Long , Will Deacon Subject: Re: [PATCH v2 1/2] seqlock: Do the lockdep annotation before locking in do_write_seqcount_begin_nested() Message-ID: <20230626125618.e52lrsmulrubrftm@techsingularity.net> References: <20230623171232.892937-1-bigeasy@linutronix.de> <20230623171232.892937-2-bigeasy@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20230623171232.892937-2-bigeasy@linutronix.de> X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 30EA3100002 X-Stat-Signature: ztxr5zdsb6q6qoyhs4cn4hkyh3was7nr X-HE-Tag: 1687784182-674617 X-HE-Meta: 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 Rwb/ZaLp GdvxTrb1nyhl3BT880xkexP8pFib5Hwl9nMkdFHdNxO/qjO2r5CAC4z3926TaJrGKkYUk4S54DXWpbLaKTX0ulzjFQ4ZnG8dL15prnqfTCrGkP4FQExzL3OcsPyIHLfxLYNCnG3Av3whUpsLxi2A9Bmj3iOWWpw+474nSj/fg0zbcOY2HUvrg924yPLvCFmiVHrSSDnyP2KzxdWHrWzrc0Slw3ZxUHjutPU33BJLw4ODGjBcTlJFV2sdH3u44IPRzefqWv8Yaj62TFNSUw2qR8hKgLh8dDwalN+yCYmVkPSvEJB2RjCsfP+2aVoutgrkMvXJdM8JqBlWhDqcVDVDsj1mc4viUmeC9r7kFuZXJRQ2P+oTtPY+CvJyY4UncYpYaEd6sFigdjf8GHfYgGAYt4+8qVA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, Jun 23, 2023 at 07:12:31PM +0200, Sebastian Andrzej Siewior wrote: > 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 > Link: https://lore.kernel.org/20230621130641.-5iueY1I@linutronix.de > Signed-off-by: Sebastian Andrzej Siewior Acked-by: Mel Gorman -- Mel Gorman SUSE Labs