Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1753506AbeADWd7 (ORCPT <rfc822;ralf@linux-mips.org> + 1 other);
        Thu, 4 Jan 2018 17:33:59 -0500
Received: from mail-it0-f43.google.com ([209.85.214.43]:36425 "EHLO
        mail-it0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1751952AbeADWd5 (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Thu, 4 Jan 2018 17:33:57 -0500
X-Google-Smtp-Source: ACJfBouykjUiLxE+9KZuX36WMhKGT0MsVG/bVRZETObIR9hivpPV7nrxH9udERAIcT/k6HGBP4eDXUkxAYXvkKLPZJE=
MIME-Version: 1.0
In-Reply-To: <CAOAebxsigJwC3zQPo=YET0NK1DZRTehngmCtM1UV__E+txcN8w@mail.gmail.com>
References: <20180103195056.837404126@linuxfoundation.org> <alpine.LSU.2.20.1801042035570.10507@er-systems.de>
 <20180104195055.GA29809@kroah.com> <alpine.LSU.2.20.1801042112380.10507@er-systems.de>
 <CA+55aFy3wKvzU9wXDrp3bzh9QbUchCEoP5AAiOkv-jvUwr0CiA@mail.gmail.com>
 <AA8653C7-EA47-4651-AE51-FCBF2ABFBBD8@amacapital.net> <CANsGZ6Zcwaz7BvDCy31z-afWOM_=vKXK-YvRErM=HOj24XUnFA@mail.gmail.com>
 <CAOAebxsfNGEsWiMbVEaTxoLSP9NMHEKvzGgoy3uvMx0EHw9BJA@mail.gmail.com>
 <CANsGZ6ZdJNxxYbARYCxNHvxwUsQTnBqZZ3SbpUS3aHg1jRF6SA@mail.gmail.com> <CAOAebxsigJwC3zQPo=YET0NK1DZRTehngmCtM1UV__E+txcN8w@mail.gmail.com>
From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Thu, 4 Jan 2018 14:33:55 -0800
X-Google-Sender-Auth: RoHN-m-vKejZoWwNjaN1UICwbhI
Message-ID: <CA+55aFwJ9dB9_xHi-ZThu1KJ1i9K9w9_va_WDOnfoAcX_FWB9g@mail.gmail.com>
Subject: Re: [PATCH 4.4 00/37] 4.4.110-stable review
To: Pavel Tatashin <pasha.tatashin@oracle.com>
Cc: Hugh Dickins <hughd@google.com>,
        Andy Lutomirski <luto@amacapital.net>,
        Thomas Voegtle <tv@lio96.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Guenter Roeck <linux@roeck-us.net>,
        Shuah Khan <shuahkh@osg.samsung.com>, patches@kernelci.org,
        Ben Hutchings <ben.hutchings@codethink.co.uk>,
        lkft-triage@lists.linaro.org, stable <stable@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Return-Path: <linux-kernel-owner@vger.kernel.org>

On Thu, Jan 4, 2018 at 1:48 PM, Pavel Tatashin
<pasha.tatashin@oracle.com> wrote:
> [    6.159992] Code: 89 83 78 06 01 00 b8 01 00 00 00 5b 41 5c 41 5d
> 5d c3 0f 1f 80 00 00 00 00 0f 1f 44 00 00 55 31 d2 48 8b 87 c8 00 00
> 00 48 89 e5 <f0> 0f c1 50 0c 89 97 d0 00 00 00 83 e2 01 b8 01 00 00 00
> 74 1d

Yeah, it's the "lock xadd" as suspected:

   0:   0f 1f 44 00 00          nopl   0x0(%rax,%rax,1)
   5:   55                      push   %rbp
   6:   31 d2                   xor    %edx,%edx
   8:   48 8b 87 c8 00 00 00    mov    0xc8(%rdi),%rax
   f:   48 89 e5                mov    %rsp,%rbp
  12:*  f0 0f c1 50 0c          lock xadd %edx,0xc(%rax)
 <-- trapping instruction
  17:   89 97 d0 00 00 00       mov    %edx,0xd0(%rdi)
  1d:   83 e2 01                and    $0x1,%edx
  20:   b8 01 00 00 00          mov    $0x1,%eax
  25:   74 1d                   je     0x44

(that first "nop" is a 5-byte nop that is used for the function
tracing placeholder).

And %rax contains garbage (the value "1", rather than a valid kernel pointer).

Sadly, I have no idea about how that garbage came about.

                Linus