From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1752306AbcAZUwu (ORCPT <rfc822;w@1wt.eu>);
	Tue, 26 Jan 2016 15:52:50 -0500
Received: from mx1.redhat.com ([209.132.183.28]:56498 "EHLO mx1.redhat.com"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1752265AbcAZUws (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Tue, 26 Jan 2016 15:52:48 -0500
Date: Tue, 26 Jan 2016 21:52:44 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: Dmitry Vyukov <dvyukov@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
        "Amanieu d'Antras" <amanieu@gmail.com>,
        Richard Weinberger <richard@nod.at>,
        Davidlohr Bueso <dave@stgolabs.net>,
        Vladimir Davydov <vdavydov@parallels.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Andy Lutomirski <luto@amacapital.net>,
        LKML <linux-kernel@vger.kernel.org>,
        syzkaller <syzkaller@googlegroups.com>,
        Kostya Serebryany <kcc@google.com>,
        Alexander Potapenko <glider@google.com>,
        Sasha Levin <sasha.levin@oracle.com>,
        Eric Dumazet <edumazet@google.com>
Subject: Re: WARNING in do_jobctl_trap
Message-ID: <20160126205244.GA4649@redhat.com>
References: <CACT4Y+Ym4AVNGo5P2E_5pV2whf-zBps+qAww=rkMA5b=o1-Mfg@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CACT4Y+Ym4AVNGo5P2E_5pV2whf-zBps+qAww=rkMA5b=o1-Mfg@mail.gmail.com>
User-Agent: Mutt/1.5.24 (2015-08-30)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On 01/26, Dmitry Vyukov wrote:
>
> Hello,
>
> The following program triggers WARN_ON_ONCE(!signr) in do_jobctl_trap:

Can't reproduce, but most probably I understand the problem... I'll try to
make the simplified test-case tomorrow, it should work if I am right.

Does it work for you reliably?  If yes, any chance you can try the patch
below?

Oleg.

--- x/kernel/ptrace.c
+++ x/kernel/ptrace.c
@@ -73,11 +73,11 @@ void __ptrace_unlink(struct task_struct *child)
 {
 	BUG_ON(!child->ptrace);
 
-	child->ptrace = 0;
 	child->parent = child->real_parent;
 	list_del_init(&child->ptrace_entry);
 
 	spin_lock(&child->sighand->siglock);
+	child->ptrace = 0;
 
 	/*
 	 * Clear all pending traps and TRAPPING.  TRAPPING should be