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 X-Spam-Level: X-Spam-Status: No, score=-7.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 65D78C4361B for ; Thu, 17 Dec 2020 15:19:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3366923976 for ; Thu, 17 Dec 2020 15:19:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728578AbgLQPTt (ORCPT ); Thu, 17 Dec 2020 10:19:49 -0500 Received: from mail.kernel.org ([198.145.29.99]:37440 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725468AbgLQPTp (ORCPT ); Thu, 17 Dec 2020 10:19:45 -0500 Date: Thu, 17 Dec 2020 07:19:04 -0800 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1608218344; bh=RSVecaGULUl9bn8yun7uAthvTLRzL5v+XNCje+IERvk=; h=From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=lSJ9bzossl6Kp+UBFKCu+RKSFSGjYPefsQRn5dzasZK1nmrEJnIBlUcglwH7E2p51 edaPnwofd6wPzu6LRoVSddXNaVlVfoicuo4Xh7kkviKlw1YDxh0ZHhomin4SljSpvv VjMOuLPywMqnywH9BLlaBaROj6AVswVl1odJMOBjh4r9QzQzIg8u8HyfcbZMv7Hkt3 NbrOu2VRbEpBO66H6v/Z9w4YiSiaFjUt9MV0ijenVcueC92bkAPQcZWTlfOGUoqopD 9EeVJSjCzdFt1+Iz1SbPUShWjNyMsZtRT8XnYU8vKE0eOFnUvvwyT2acc96PU6wfg7 3xtgLjVfNkpAQ== From: "Paul E. McKenney" To: Dmitry Vyukov Cc: Matthew Wilcox , Peter Zijlstra , Ingo Molnar , Will Deacon , syzbot , linux-fsdevel , LKML , syzkaller-bugs , Al Viro Subject: Re: WARNING: suspicious RCU usage in count Message-ID: <20201217151904.GQ2657@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <0000000000009867cb05b699f5b6@google.com> <20201216205536.GX2443@casper.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Dec 17, 2020 at 09:26:44AM +0100, Dmitry Vyukov wrote: > On Wed, Dec 16, 2020 at 9:55 PM Matthew Wilcox wrote: > > > > On Wed, Dec 16, 2020 at 11:34:10AM -0800, syzbot wrote: > > > Unfortunately, I don't have any reproducer for this issue yet. > > > > > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > > > Reported-by: syzbot+51ce7a5794c3b12a70d1@syzkaller.appspotmail.com > > > > > > ============================= > > > WARNING: suspicious RCU usage > > > 5.10.0-rc7-syzkaller #0 Not tainted > > > ----------------------------- > > > kernel/sched/core.c:7270 Illegal context switch in RCU-bh read-side critical section! > > > > > > other info that might help us debug this: > > > > > > > > > rcu_scheduler_active = 2, debug_locks = 0 > > > no locks held by udevd/9038. > > > > > > stack backtrace: > > > CPU: 3 PID: 9038 Comm: udevd Not tainted 5.10.0-rc7-syzkaller #0 > > > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu.org 04/01/2014 > > > Call Trace: > > > __dump_stack lib/dump_stack.c:77 [inline] > > > dump_stack+0x107/0x163 lib/dump_stack.c:118 > > > ___might_sleep+0x220/0x2b0 kernel/sched/core.c:7270 > > > count.constprop.0+0x164/0x270 fs/exec.c:449 > > > do_execveat_common+0x2fd/0x7c0 fs/exec.c:1893 > > > do_execve fs/exec.c:1983 [inline] > > > __do_sys_execve fs/exec.c:2059 [inline] > > > __se_sys_execve fs/exec.c:2054 [inline] > > > __x64_sys_execve+0x8f/0xc0 fs/exec.c:2054 > > > do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46 > > > > This must be the victim of something else. There's no way this call > > trace took the RCU read lock. > > +lockdep maintainers for lockdep false positive then and +Paul for rcu Note that this was "RCU-bh" rather than "RCU", so it might be something like local_bh_disable() rather than rcu_read_lock() that might_sleep() is complaining about. > There is another recent claim of a false "suspicious RCU usage": > https://lore.kernel.org/lkml/CAKMK7uEiS5SrBYv-2w2wWL=9G4ByoHvtiWVsPqekswZzOGmzjg@mail.gmail.com/ That one does look familiar. ;-) Thanx, Paul