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=-2.4 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham 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 8E57DC04A6B for ; Mon, 6 May 2019 16:50:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 63BCB20830 for ; Mon, 6 May 2019 16:50:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726646AbfEFQuU (ORCPT ); Mon, 6 May 2019 12:50:20 -0400 Received: from mx1.redhat.com ([209.132.183.28]:32938 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725883AbfEFQuU (ORCPT ); Mon, 6 May 2019 12:50:20 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id C2BB07E43D; Mon, 6 May 2019 16:50:19 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.43.17.159]) by smtp.corp.redhat.com (Postfix) with SMTP id B47F75EDE4; Mon, 6 May 2019 16:50:10 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Mon, 6 May 2019 18:50:19 +0200 (CEST) Date: Mon, 6 May 2019 18:50:09 +0200 From: Oleg Nesterov To: Peter Zijlstra Cc: Sebastian Andrzej Siewior , linux-rt-users , LKML , Thomas Gleixner , Daniel Bristot de Oliveira , Clark Williams , Juri Lelli , jack@suse.com, Waiman Long , Davidlohr Bueso Subject: Re: [RT WARNING] DEBUG_LOCKS_WARN_ON(rt_mutex_owner(lock) != current) with fsfreeze (4.19.25-rt16) Message-ID: <20190506165009.GA28959@redhat.com> References: <20190326093421.GA29508@localhost.localdomain> <20190419085627.GI4742@localhost.localdomain> <20190430125130.uw7mhdnsoqr2v3gf@linutronix.de> <20190430132811.GB2589@hirez.programming.kicks-ass.net> <20190501170953.GB2650@hirez.programming.kicks-ass.net> <20190502100932.GA7323@redhat.com> <20190502114258.GB7323@redhat.com> <20190503145059.GC2606@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190503145059.GC2606@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.27]); Mon, 06 May 2019 16:50:20 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/03, Peter Zijlstra wrote: > > -static void lockdep_sb_freeze_release(struct super_block *sb) > -{ > - int level; > - > - for (level = SB_FREEZE_LEVELS - 1; level >= 0; level--) > - percpu_rwsem_release(sb->s_writers.rw_sem + level, 0, _THIS_IP_); > -} > - > -/* > - * Tell lockdep we are holding these locks before we call ->unfreeze_fs(sb). > - */ > -static void lockdep_sb_freeze_acquire(struct super_block *sb) > -{ > - int level; > - > - for (level = 0; level < SB_FREEZE_LEVELS; ++level) > - percpu_rwsem_acquire(sb->s_writers.rw_sem + level, 0, _THIS_IP_); > + percpu_down_write_non_owner(sb->s_writers.rw_sem + level-1); > } I'd suggest to not change fs/super.c, keep these helpers, and even not introduce xxx_write_non_owner(). freeze_super() takes other locks, it calls sync_filesystem(), freeze_fs(), lockdep should know that this task holds SB_FREEZE_XXX locks for writing. > @@ -80,14 +83,8 @@ int __percpu_down_read(struct percpu_rw_ > * and reschedule on the preempt_enable() in percpu_down_read(). > */ > preempt_enable_no_resched(); > - > - /* > - * Avoid lockdep for the down/up_read() we already have them. > - */ > - __down_read(&sem->rw_sem); > + wait_event(sem->waiters, !atomic_read(&sem->block)); > this_cpu_inc(*sem->read_count); Argh, this looks racy :/ Suppose that sem->block == 0 when wait_event() is called, iow the writer released the lock. Now suppose that this __percpu_down_read() races with another percpu_down_write(). The new writer can set sem->block == 1 and call readers_active_check() in between, after wait_event() and before this_cpu_inc(*sem->read_count). Oleg.