Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161934AbbKEPMP (ORCPT ); Thu, 5 Nov 2015 10:12:15 -0500 Received: from mx1.redhat.com ([209.132.183.28]:52668 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1161471AbbKEPMO (ORCPT ); Thu, 5 Nov 2015 10:12:14 -0500 Date: Thu, 5 Nov 2015 17:08:22 +0100 From: Oleg Nesterov To: Andrew Morton Cc: Dmitry Vyukov , Roland McGrath , amanieu@gmail.com, pmoore@redhat.com, Ingo Molnar , vdavydov@parallels.com, qiaowei.ren@intel.com, dave@stgolabs.net, palmer@dabbelt.com, LKML , syzkaller , Kostya Serebryany , Alexander Potapenko , Sasha Levin Subject: Re: [PATCH 1/1] signal: kill the obsolete SIGNAL_UNKILLABLE check in complete_signal() Message-ID: <20151105160822.GA26017@redhat.com> References: <20151102151333.GA17152@redhat.com> <20151102163654.GA18804@redhat.com> <20151102180624.GA24361@redhat.com> <20151104191804.GA20578@redhat.com> <20151104191912.GB20578@redhat.com> <20151104172123.590fcbf0e8904911eeab3e3d@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20151104172123.590fcbf0e8904911eeab3e3d@linux-foundation.org> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1685 Lines: 50 On 11/04, Andrew Morton wrote: > > On Wed, 4 Nov 2015 20:19:12 +0100 Oleg Nesterov wrote: > > > This explains WARN_ON(!JOBCTL_STOP_PENDING) in task_participate_group_stop() > > triggered by the test-case from Dmitry: > > > > int main() > > { > > int pid = 1; > > ptrace(PTRACE_ATTACH, pid, 0, 0); > > ptrace(PTRACE_SETOPTIONS, pid, 0, PTRACE_O_EXITKILL); > > sleep(1); > > return 0; > > } ... > > The test-case above needs root and (correctly) crashes the kernel, > I'm thinking this should be backported into -stable due to WARN_ONs and > kernel crashes. Ah, sorry for confusion. The kernel crash is fine/correct. Debugger kills init process, the exiting init calls panic(). With or without this patch. BTW, I always thought we should remove this panic(), but this is off-topic. After this patch the test-case above still crashes the kernel, but without warning ;) > And as f008faff0e27 is from 2009, that means all > kernels. Yes, I think this change is safe for -stable. But the only visible problem is WARN_ON_ONCE() in task_participate_group_stop(), so I am not sure... Well. Actually there are more problems. zap_threads(), de_thread() can be fooled by signal_group_exit() == F too. So a multi-threaded /sbin/init can miss SIGKILL if it does execve(), or if it starts the coredump. But only if SIGKILL was private (sent by tkill). I do not see any serious problem this patch could fix. Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/