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 2647AC636CC for ; Sun, 5 Feb 2023 00:22:17 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 1B0126B0072; Sat, 4 Feb 2023 19:22:17 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 15FFD6B0073; Sat, 4 Feb 2023 19:22:17 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 04F3B6B0074; Sat, 4 Feb 2023 19:22:17 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id ECA5E6B0072 for ; Sat, 4 Feb 2023 19:22:16 -0500 (EST) Received: from smtpin08.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id B62E314059B for ; Sun, 5 Feb 2023 00:22:16 +0000 (UTC) X-FDA: 80431336272.08.46E3AD2 Received: from r3-22.sinamail.sina.com.cn (r3-22.sinamail.sina.com.cn [202.108.3.22]) by imf24.hostedemail.com (Postfix) with ESMTP id 097AF180002 for ; Sun, 5 Feb 2023 00:22:11 +0000 (UTC) Authentication-Results: imf24.hostedemail.com; dkim=none; dmarc=none; spf=pass (imf24.hostedemail.com: domain of hdanton@sina.com designates 202.108.3.22 as permitted sender) smtp.mailfrom=hdanton@sina.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1675556534; 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-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=d0EnDZS6pYUi1AK4zcmu3fjswnghZcdQXR4eDgp10iY=; b=r511Dq29Zm3kFGwoodBB5/eihhOAuWxoml6SZWpaiUvXC73V4B/UqSruTUUYeASnetlBqv e4cXXawqrGvza/2QAZVH6naNzUXClPzOisW626NaMq4JIa3QfL9gQKmK8dG3VHAn79jvPh QwlyFrGrf/7vPsrNq+2TiC1R9Dp/MYw= ARC-Authentication-Results: i=1; imf24.hostedemail.com; dkim=none; dmarc=none; spf=pass (imf24.hostedemail.com: domain of hdanton@sina.com designates 202.108.3.22 as permitted sender) smtp.mailfrom=hdanton@sina.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1675556534; a=rsa-sha256; cv=none; b=eE7DzSwb/fXpDBsJkUR3r4Q3xH7efN80PtqwHRoZLsNxzmxfh9cICba5TsZBZAw1ZRQL/x sIS/G4AQeMUSTjUaGrPiwthuk7U7bRfr/4N39NE5h5jyVZ3lYhPwJ8Kg0fx2lO3zJ8OJFp bShePMKVhJ5aat///asW2sKyebeuQOI= Received: from unknown (HELO localhost.localdomain)([114.249.61.130]) by sina.com (172.16.97.32) with ESMTP id 63DEF5B600030B70; Sun, 5 Feb 2023 08:17:59 +0800 (CST) X-Sender: hdanton@sina.com X-Auth-ID: hdanton@sina.com X-SMAIL-MID: 608695630093 From: Hillf Danton To: Alan Stern Cc: Tetsuo Handa , Greg Kroah-Hartman , "Rafael J. Wysocki" , Linus Torvalds , LKML , linux-mm@kvack.org, USB list Subject: Re: Converting dev->mutex into dev->spinlock ? Date: Sun, 5 Feb 2023 08:21:56 +0800 Message-Id: <20230205002156.1071-1-hdanton@sina.com> In-Reply-To: References: <28a82f50-39d5-a45f-7c7a-57a66cec0741@I-love.SAKURA.ne.jp> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 097AF180002 X-Rspamd-Server: rspam09 X-Rspam-User: X-Stat-Signature: m1xjfhydwnw9x57r9oxqx571q9itcmkc X-HE-Tag: 1675556531-329451 X-HE-Meta: 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 H6PAiYe8 D/gRh8t0b9+E7sZtFBBZWdqTCNyBVtPNliMtb3nAcyFLtPaHidWlWz2W1gyIvMXR+fw87sQL+lXXZL8qxtAED87/x/0lnow9P0FOPjFCspmogkhCYFCvB9J4qTjSG/sg7bZiS5mZsc7ZwPe5Z078ajFkjH0Sbqul3SN3sjzaTgTPpobzGcasMegnOV/u886Lfn9hAjIKIOTy0P8e+bqr2hAW8IdyAdbhQ8nAINgBXn15BSEMvIH9L+eBeU9MoHb9XN30w 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 Sat, 4 Feb 2023 10:40:52 -0500 Alan Stern > On Sun, Feb 05, 2023 at 12:30:07AM +0900, Tetsuo Handa wrote: > > On 2023/02/05 0:12, Alan Stern wrote: > > >> it would solve many deadlocks in driver code if you can update > > > > > > What deadlocks? If there are so many deadlocks floating around in > > > driver code, why haven't we heard about them before now? > > > > Since dev->mutex is hidden from lockdep checks, nobody can see lockdep warnings. > > syzbot is reporting real deadlocks without lockdep warnings, for the fundamental > > problem you mentioned in https://lkml.kernel.org/r/Pine.LNX.4.44L0.0804171117450.18040-100000@iolanthe.rowland.org > > is remaining. I'm suggesting you that now is time to address this fundamental problem. > > Maybe so. But the place to address it is inside lockdep, not in the > driver core. > > > >> (by e.g. replacing dev->mutex with dev->spinlock and dev->atomic_flags). > > >> But I'm not familiar enough to propose such change... > > > > > > Such a change cannot be made. Consider this: Driver callbacks often > > > need to sleep. But when a thread holds a spinlock, it is not allowed to > > > sleep. Therefore driver callbacks must not be invoked while a spinlock > > > is held. > > > > What I'm suggesting is "Do not call driver callbacks with dev->mutex held, > > by rewriting driver core code". > > That cannot be done. The only possible solution is to teach lockdep how > to handle recursive locking structures. It works in dcache - see the slow path in dentry_kill() for instance. Hillf