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=-10.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SPF_HELO_NONE,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 459A2C04AB3 for ; Mon, 27 May 2019 15:45:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2926D20815 for ; Mon, 27 May 2019 15:45:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726823AbfE0PpK (ORCPT ); Mon, 27 May 2019 11:45:10 -0400 Received: from mga07.intel.com ([134.134.136.100]:33673 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726322AbfE0PpI (ORCPT ); Mon, 27 May 2019 11:45:08 -0400 X-Amp-Result: UNSCANNABLE X-Amp-File-Uploaded: False Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by orsmga105.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 27 May 2019 08:45:07 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.60,519,1549958400"; d="scan'208";a="178926384" Received: from ideak-desk.fi.intel.com ([10.237.72.204]) by fmsmga002.fm.intel.com with ESMTP; 27 May 2019 08:45:05 -0700 Date: Mon, 27 May 2019 18:44:29 +0300 From: Imre Deak To: Peter Zijlstra Cc: LKML , Ville =?iso-8859-1?Q?Syrj=E4l=E4?= , Ingo Molnar , Will Deacon Subject: Re: [PATCH v2 2/2] lockdep: Fix merging of hlocks with non-zero references Message-ID: <20190527154429.GC24536@ideak-desk.fi.intel.com> Reply-To: imre.deak@intel.com References: <20190524201509.9199-1-imre.deak@intel.com> <20190524201509.9199-2-imre.deak@intel.com> <20190527151438.GF2623@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190527151438.GF2623@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, May 27, 2019 at 05:14:38PM +0200, Peter Zijlstra wrote: > On Fri, May 24, 2019 at 11:15:09PM +0300, Imre Deak wrote: > > diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c > > index 967352d32af1..9e2a4ab6c731 100644 > > --- a/kernel/locking/lockdep.c > > +++ b/kernel/locking/lockdep.c > > @@ -3637,6 +3637,11 @@ print_lock_nested_lock_not_held(struct task_struct *curr, > > > > static int __lock_is_held(const struct lockdep_map *lock, int read); > > > > +static int hlock_reference(int reference) > > +{ > > + return reference ? : 1; > > +} > > + > > /* > > * This gets called for every mutex_lock*()/spin_lock*() operation. > > * We maintain the dependency maps and validate the locking attempt: > > @@ -3702,17 +3707,15 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass, > > if (depth) { > > hlock = curr->held_locks + depth - 1; > > if (hlock->class_idx == class_idx && nest_lock) { > > - if (hlock->references) { > > - /* > > - * Check: unsigned int references overflow. > > - */ > > - if (DEBUG_LOCKS_WARN_ON(hlock->references == UINT_MAX)) > > What tree is this against? I just used our git://anongit.freedesktop.org/drm-tip and the most recent upstream commit in that is: $ git merge-base drm-tip origin/master 6b0538da5a6ca2129b93cea5afc997226875c402 which has the commit commit a188339ca5a396acc588e5851ed7e19f66b0ebd9 Author: Linus Torvalds Date: Sun May 19 15:47:09 2019 -0700 Linux 5.2-rc1 > Afaict this is still 12 bits ?! In the above tree I see unsigned int references; in held_lock which is 32 bits. > > > - return 0; > > + /* > > + * Check: unsigned int references overflow. > > + */ > > + if (DEBUG_LOCKS_WARN_ON(hlock_reference(hlock->references) > > > + UINT_MAX - hlock_reference(references))) > > Idem. Also very weird overflow check.. We could have instead (replacing the addition itself too below): if (DEBUG_LOCKS_WARN_ON( check_add_overflow(hlock_reference(hlock->references), hlock_reference(references), &hlock_references))) return 0; by having hlock_reference() take and return unsigned int too. > > > + return 0; > > > > - hlock->references++; > > - } else { > > - hlock->references = 2; > > - } > > + hlock->references = hlock_reference(hlock->references) + > > + hlock_reference(references); > > > > return 2; > > } > > -- > > 2.17.1 > >