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 S1755463AbcA2LzA (ORCPT <rfc822;w@1wt.eu>);
	Fri, 29 Jan 2016 06:55:00 -0500
Received: from www.linutronix.de ([62.245.132.108]:54300 "EHLO
	Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1753090AbcA2Ly7 (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Fri, 29 Jan 2016 06:54:59 -0500
Date: Fri, 29 Jan 2016 12:53:48 +0100 (CET)
From: Thomas Gleixner <tglx@linutronix.de>
To: Dmitry Vyukov <dvyukov@google.com>
cc: Oleg Nesterov <oleg@redhat.com>, Andrew Morton <akpm@linux-foundation.org>,
        Richard Weinberger <richard@nod.at>,
        "Amanieu d'Antras" <amanieu@gmail.com>,
        Chris Metcalf <cmetcalf@ezchip.com>,
        Andy Lutomirski <luto@amacapital.net>,
        Davidlohr Bueso <dave@stgolabs.net>,
        Vladimir Davydov <vdavydov@parallels.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        LKML <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: WARNING in set_restore_sigmask
In-Reply-To: <CACT4Y+a+O5MXtZd5U-3t_7vQFhGaRCwMhrTB5OCcN5s=i4sTJg@mail.gmail.com>
Message-ID: <alpine.DEB.2.11.1601291246340.3886@nanos>
References: <CACT4Y+a+O5MXtZd5U-3t_7vQFhGaRCwMhrTB5OCcN5s=i4sTJg@mail.gmail.com>
User-Agent: Alpine 2.11 (DEB 23 2013-08-11)
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII
X-Linutronix-Spam-Score: -1.0
X-Linutronix-Spam-Level: -
X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required,  ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

Dmitry,

On Fri, 29 Jan 2016, Dmitry Vyukov wrote:
> WARNING: CPU: 2 PID: 10905 at ./arch/x86/include/asm/thread_info.h:236
> sigsuspend+0x18e/0x1f0()
> Modules linked in:
> CPU: 2 PID: 10905 Comm: syz-executor Not tainted 4.5.0-rc1+ #300
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
>  00000000ffffffff ffff88006139fe38 ffffffff82be118d 0000000000000000
>  ffff88006d054740 ffffffff867387e0 ffff88006139fe78 ffffffff813536d9
>  ffffffff813839ce ffffffff867387e0 00000000000000ec 0000000020000000
> Call Trace:
>  [<     inline     >] __dump_stack lib/dump_stack.c:15
>  [<ffffffff82be118d>] dump_stack+0x6f/0xa2 lib/dump_stack.c:50
>  [<ffffffff813536d9>] warn_slowpath_common+0xd9/0x140 kernel/panic.c:482
>  [<ffffffff81353909>] warn_slowpath_null+0x29/0x30 kernel/panic.c:515
>  [<     inline     >] set_restore_sigmask
> ./arch/x86/include/asm/thread_info.h:236
>  [<ffffffff813839ce>] sigsuspend+0x18e/0x1f0 kernel/signal.c:3513
>  [<     inline     >] SYSC_rt_sigsuspend kernel/signal.c:3533
>  [<ffffffff81387d7c>] SyS_rt_sigsuspend+0xac/0xe0 kernel/signal.c:3523
>  [<ffffffff86653236>] entry_SYSCALL_64_fastpath+0x16/0x7a
> arch/x86/entry/entry_64.S:185
> ---[ end trace da5c27e3b7defd96 ]---

That could be just a spurious wakeup of unknown provenience. The sigsuspend
code has no protection against those. I can't see why that happens ...

> Unfortunately I cannot reproduce it. But the only two programs that

I would be helpful if you could run your fuzzers with a minimal set of trace
points enabled (raw_syscalls, sched events) and set
/proc/sys/kernel/traceoff_on_warning to 1, so the trace freezes when a warning
is triggered.

That might give us at least some insight into these one off issues.

Thanks,

	tglx