From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752627AbdKFM03 (ORCPT ); Mon, 6 Nov 2017 07:26:29 -0500 Received: from aserp1040.oracle.com ([141.146.126.69]:28607 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751717AbdKFM02 (ORCPT ); Mon, 6 Nov 2017 07:26:28 -0500 Date: Mon, 6 Nov 2017 12:26:05 +0000 From: Jamie Iles To: Dmitry Vyukov Cc: Jamie Iles , Oleg Nesterov , syzbot , Andrew Morton , Arvind Yadav , Mark Brown , "Eric W. Biederman" , =?iso-8859-1?Q?Fr=E9d=E9ric?= Weisbecker , LKML , "Martin K. Petersen" , mchehab@kernel.org, Ingo Molnar , mpe@ellerman.id.au, syzkaller-bugs@googlegroups.com, Al Viro , Kyle Huey , Kees Cook Subject: Re: WARNING in task_participate_group_stop Message-ID: <20171106122605.zdqjodn3wtcjqevh@cedar> References: <94eb2c058c80ea49ed055cc8695e@google.com> <20171031163451.GA30223@redhat.com> <20171102170138.GA13663@redhat.com> <20171106112508.lun6eftpj5icnvdy@cedar> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20170113 (1.7.2) X-Source-IP: aserv0021.oracle.com [141.146.126.233] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Nov 06, 2017 at 12:56:09PM +0100, Dmitry Vyukov wrote: > On Mon, Nov 6, 2017 at 12:25 PM, Jamie Iles wrote: > > Hi Dmitry, > > > > On Mon, Nov 06, 2017 at 12:02:19PM +0100, Dmitry Vyukov wrote: > >> On Thu, Nov 2, 2017 at 6:01 PM, Oleg Nesterov wrote: > >> > On 11/01, Dmitry Vyukov wrote: > >> >> > >> >> On Tue, Oct 31, 2017 at 7:34 PM, Oleg Nesterov wrote: > >> >> > Hmm. I do not see reproducer in this email... > >> >> > >> >> Ah, sorry. You can see full thread with attachments here: > >> >> https://groups.google.com/forum/#!topic/syzkaller-bugs/EUmYZU4m5gU > >> > > >> > Heh. I can't say I enjoyed reading the reproducer ;) > >> > > >> >> >> > WARNING: CPU: 0 PID: 1 at kernel/signal.c:340 > >> >> >> > task_participate_group_stop+0x1ce/0x230 kernel/signal.c:340 > >> >> >> > Kernel panic - not syncing: panic_on_warn set ... > >> >> >> > > >> >> >> > CPU: 0 PID: 1 Comm: init Not tainted 4.13.0-mm1+ #5 > >> >> > > >> >> > So this is init process with SIGNAL_UNKILLABLE flag set. And I hope it has > >> >> > the pending SIGKILL, otherwise there is something else. > >> > > >> > From repro.c > >> > > >> > line 111 r[8] = syscall(__NR_ptrace, 0x10ul, r[7]); > >> > > >> > this is PTRACE_ATTACH > >> > > >> > line 115 syscall(__NR_ptrace, 0x4200ul, r[7], 0x40000012ul, 0x100012ul); > >> > > >> > this is PTRACE_SETOPTIONS and "data" includes PTRACE_O_EXITKILL. > >> > > >> > r[7] is initialized at > >> > > >> > line 110 r[7] = *(uint32_t*)0x20f9cffc; > >> > > >> > so if it is eq to 1 then it can attach to init and in this case the problem > >> > can be explained by the wrong SIGNAL_UNKILLABLE/SIGKILL logic. > >> > > >> > But how *(uint32_t*)0x20f9cffc can be 1 ? > >> > > >> > line 108 r[6] = syscall(__NR_fcntl, r[1], 0x10ul, 0x20f9cff8ul); > >> > > >> > this is F_GETOWN_EX, addr = 0x20f9cff8 == 0x20f9cffc + 4, so if fcntl() > >> > actually succeeds then r[7] == f_owner_ex->pid. > >> > > >> > It _can_ be 1, but the reproducer doesn't work for me. If you can reproduce, > >> > could you try the patch below? > >> > >> Hi, > >> > >> I would like to understand why you were not able to reproduce it. I > >> won't be sitting here all the time, and we are tracking hundreds of > >> bugs across different linux kernels and other OSes, so it's > >> problematic to do any extensive work on all of them. That's why we try > >> to provide reproducers. > >> > >> I've just tried the repro on the latest upstream > >> (39dae59d66acd86d1de24294bd2f343fd5e7a625) and it triggered the > >> WARNING within a second. > >> Did you use the config provided? Did you use qemu or real hardware? > >> Can you try in qemu (with -smp>1)? > > > > I'm unable to reproduce the warning in qemu with SMP (on a 32 CPU VM). > > Instead I get the following instant traceback which is different to what > > you report when run as root: > > > Uh, it seems to be racy. I am getting either the WARNING or "attempt > to kill init" in ~1/5 proportion. > Please try this simplified program, it triggers the WARNING all the time for me: I can't reproduce the warning with that reproducer, but I do see that it runs and exits once and init is left in state T then the second run ends up killing init and the VM crashes. If I run once and then 'kill -CONT 1' then init goes back to sleeping and won't accept a SIGSTOP so it looks like SIGNAL_UNKILLABLE isn't gone though. Jamie