From mboxrd@z Thu Jan 1 00:00:00 1970 Content-Type: multipart/mixed; boundary="===============0645165766634388027==" MIME-Version: 1.0 From: Ingo Molnar To: lkp@lists.01.org Subject: Re: [lockdep] b09be676e0 BUG: unable to handle kernel NULL pointer dereference at 000001f2 Date: Tue, 03 Oct 2017 19:18:24 +0200 Message-ID: <20171003171824.te5cxms2hq634tvi@gmail.com> In-Reply-To: List-Id: --===============0645165766634388027== Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable * Linus Torvalds wrote: > On Tue, Oct 3, 2017 at 7:06 AM, Fengguang Wu w= rote: > > > > This patch triggers a NULL-dereference bug at update_stack_state(). > > Although its parent commit also has a NULL-dereference bug, however > > the call stack looks rather different. Both dmesg files are attached. > > > > It also triggers this warning, which is being discussed in another > > thread, so CC Josh. The full dmesg attached, too. > > > > Please press Enter to activate this console. > > [ 138.605622] WARNING: kernel stack regs at be299c9a in procd:= 340 has bad 'bp' value 000001be > > [ 138.605627] unwind stack type:0 next_sp: (null) mask:0x2 gr= aph_idx:0 > > [ 138.605631] be299c9a: 299ceb00 (0x299ceb00) > > [ 138.605633] be299c9e: 2281f1be (0x2281f1be) > > [ 138.605634] be299ca2: 299cebb6 (0x299cebb6) > > > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git mast= er > > > > commit b09be676e0ff25bd6d2e7637e26d349f9109ad75 > > locking/lockdep: Implement the 'crossrelease' feature > = > Can we consider just reverting the crossrelease thing? Yes, I'll do that tomorrow. I was always a bit unhappy about cross-release, = because it breaks the 'owner task owns the lock' model. Plus I don't think we found that many real bugs with it - in a 20+ years old, 15+ MLOC code base that never run with such a debugging facility enabled. Thanks, Ingo --===============0645165766634388027==-- From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751255AbdJCRS3 (ORCPT ); Tue, 3 Oct 2017 13:18:29 -0400 Received: from mail-wm0-f66.google.com ([74.125.82.66]:57008 "EHLO mail-wm0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751072AbdJCRS2 (ORCPT ); Tue, 3 Oct 2017 13:18:28 -0400 X-Google-Smtp-Source: AOwi7QCjUZybEgWQmVTGRY/9UpeTCTmc/G7THrHolrHu3ipBB10wL+NnM9G3HbmgNAFmBSpG1m716A== Date: Tue, 3 Oct 2017 19:18:24 +0200 From: Ingo Molnar To: Linus Torvalds Cc: Fengguang Wu , Byungchul Park , "Peter Zijlstra (Intel)" , Linux Kernel Mailing List , LKP , Josh Poimboeuf Subject: Re: [lockdep] b09be676e0 BUG: unable to handle kernel NULL pointer dereference at 000001f2 Message-ID: <20171003171824.te5cxms2hq634tvi@gmail.com> References: <20171003140634.r2jzujgl62ox4uzh@wfg-t540p.sh.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20170113 (1.7.2) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Linus Torvalds wrote: > On Tue, Oct 3, 2017 at 7:06 AM, Fengguang Wu wrote: > > > > This patch triggers a NULL-dereference bug at update_stack_state(). > > Although its parent commit also has a NULL-dereference bug, however > > the call stack looks rather different. Both dmesg files are attached. > > > > It also triggers this warning, which is being discussed in another > > thread, so CC Josh. The full dmesg attached, too. > > > > Please press Enter to activate this console. > > [ 138.605622] WARNING: kernel stack regs at be299c9a in procd:340 has bad 'bp' value 000001be > > [ 138.605627] unwind stack type:0 next_sp: (null) mask:0x2 graph_idx:0 > > [ 138.605631] be299c9a: 299ceb00 (0x299ceb00) > > [ 138.605633] be299c9e: 2281f1be (0x2281f1be) > > [ 138.605634] be299ca2: 299cebb6 (0x299cebb6) > > > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master > > > > commit b09be676e0ff25bd6d2e7637e26d349f9109ad75 > > locking/lockdep: Implement the 'crossrelease' feature > > Can we consider just reverting the crossrelease thing? Yes, I'll do that tomorrow. I was always a bit unhappy about cross-release, because it breaks the 'owner task owns the lock' model. Plus I don't think we found that many real bugs with it - in a 20+ years old, 15+ MLOC code base that never run with such a debugging facility enabled. Thanks, Ingo