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 S1753226AbcEYG3D (ORCPT <rfc822;w@1wt.eu>);
	Wed, 25 May 2016 02:29:03 -0400
Received: from mail-wm0-f68.google.com ([74.125.82.68]:34929 "EHLO
	mail-wm0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1750797AbcEYG3B (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Wed, 25 May 2016 02:29:01 -0400
Date: Wed, 25 May 2016 08:28:15 +0200
From: Ingo Molnar <mingo@kernel.org>
To: Dave Jones <davej@codemonkey.org.uk>,
        kernel test robot <fengguang.wu@intel.com>,
        Borislav Petkov <bp@suse.de>, LKP <lkp@01.org>,
        oprofile-list@lists.sf.net, linux-kernel@vger.kernel.org,
        wfg@linux.intel.com
Subject: Re: [x86/cpufeature] 7b5e74e637:  BUG: unable to handle kernel
 paging request at 6b636170
Message-ID: <20160525062815.GA31368@gmail.com>
References: <5744b252.TKkyCAKRsZqh/9JL%fengguang.wu@intel.com>
 <20160524200709.GA9079@codemonkey.org.uk>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20160524200709.GA9079@codemonkey.org.uk>
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


* Dave Jones <davej@codemonkey.org.uk> wrote:

> On Wed, May 25, 2016 at 03:58:10AM +0800, kernel test robot wrote:
>  
>  > 0day kernel testing robot got the below dmesg and the first bad commit is
>  > 
>  > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
>  > 
>  > commit 7b5e74e637e4a977c7cf40fd7de332f60b68180e
>  > Author:     Borislav Petkov <bp@suse.de>
>  > AuthorDate: Tue Mar 29 17:41:54 2016 +0200
>  > Commit:     Ingo Molnar <mingo@kernel.org>
>  > CommitDate: Thu Mar 31 13:33:17 2016 +0200
>  > 
>  >     x86/cpufeature: Remove cpu_has_arch_perfmon
>  >     
>  >     Use boot_cpu_has() instead.
> 
> This seem an unlikely candidate given...
> 
>  > [    1.914984] random: trinity urandom read with 25 bits of entropy available
>  > [    8.542178] random: nonblocking pool is initialized
>  > [   11.939833] sock: process `trinity-main' is using obsolete setsockopt SO_BSDCOMPAT
>  > [   12.349890] BUG: unable to handle kernel paging request at 6b636170
>  > [   12.349895] IP: [<c108154b>] perf_prepare_sample+0x7d/0x263
> 
> The trace is more related to perf.

Also, 7b5e74e637e4a appears to be pretty much a provable NOP, it should not change 
a single byte in the kernel image, as it replaces a macro use:

-#define cpu_has_arch_perfmon   boot_cpu_has(X86_FEATURE_ARCH_PERFMON)

... with open-coded expressions of the same.

Thanks,

	Ingo