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=-3.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_NEOMUTT autolearn=unavailable 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 00D41C43219 for ; Tue, 30 Apr 2019 13:45:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CC74221670 for ; Tue, 30 Apr 2019 13:45:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726294AbfD3Npv convert rfc822-to-8bit (ORCPT ); Tue, 30 Apr 2019 09:45:51 -0400 Received: from Galois.linutronix.de ([146.0.238.70]:47342 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726053AbfD3Npv (ORCPT ); Tue, 30 Apr 2019 09:45:51 -0400 Received: from bigeasy by Galois.linutronix.de with local (Exim 4.80) (envelope-from ) id 1hLT4u-0000OZ-9a; Tue, 30 Apr 2019 15:45:48 +0200 Date: Tue, 30 Apr 2019 15:45:48 +0200 From: Sebastian Andrzej Siewior To: Peter Zijlstra Cc: linux-rt-users , LKML , Thomas Gleixner , Daniel Bristot de Oliveira , Clark Williams , Juri Lelli , Oleg Nesterov , jack@suse.com Subject: Re: [RT WARNING] DEBUG_LOCKS_WARN_ON(rt_mutex_owner(lock) != current) with fsfreeze (4.19.25-rt16) Message-ID: <20190430134547.lll7kjrslh3zat2b@linutronix.de> References: <20190326093421.GA29508@localhost.localdomain> <20190419085627.GI4742@localhost.localdomain> <20190430125130.uw7mhdnsoqr2v3gf@linutronix.de> <20190430132811.GB2589@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8BIT In-Reply-To: <20190430132811.GB2589@hirez.programming.kicks-ass.net> User-Agent: NeoMutt/20180716 Sender: linux-rt-users-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-rt-users@vger.kernel.org On 2019-04-30 15:28:11 [+0200], Peter Zijlstra wrote: > On Tue, Apr 30, 2019 at 02:51:31PM +0200, Sebastian Andrzej Siewior wrote: > > On 2019-04-19 10:56:27 [+0200], Juri Lelli wrote: > > > On 26/03/19 10:34, Juri Lelli wrote: > > > > Hi, > > > > > > > > Running this reproducer on a 4.19.25-rt16 kernel (with lock debugging > > > > turned on) produces warning below. > > > > > > And I now think this might lead to an actual crash. > > > > Peter, could you please take a look at the thread: > > https://lkml.kernel.org/r/20190419085627.GI4742@localhost.localdomain > > > > I assumed that returning to userland with acquired locks is something we > > did not want… > > Yeah, but AFAIK fs freezing code has a history of doing exactly that.. > This is just the latest incarnation here. > > So the immediate problem here is that the task doing thaw isn't the same > that did freeze, right? The thing is, I'm not seeing how that isn't a > problem with upstream either. > > The freeze code seems to do: percpu_down_write() for the various states, > and then frobs lockdep state. > > Thaw then does the reverse, frobs lockdep and then does: percpu_up_write(). > > percpu_down_write() directly relies on down_write(), and > percpu_up_write() on up_write(). And note how __up_write() has: > > DEBUG_RWSEMS_WARN_ON(sem->owner != current, sem); > > So why isn't this same code coming unstuck in mainline? I have to re-route most of this questions to Juri Lelli. Lockdep has these gems: lockdep_sb_freeze_release() / lockdep_sb_freeze_acquire() Sebastian