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 S1754910AbcITNos (ORCPT <rfc822;w@1wt.eu>);
        Tue, 20 Sep 2016 09:44:48 -0400
Received: from mga07.intel.com ([134.134.136.100]:17241 "EHLO mga07.intel.com"
        rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
        id S1752263AbcITNoq (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
        Tue, 20 Sep 2016 09:44:46 -0400
X-ExtLoop1: 1
X-IronPort-AV: E=Sophos;i="5.30,368,1470726000"; 
   d="scan'208";a="1033673217"
From: Alexander Shishkin <alexander.shishkin@linux.intel.com>
To: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>,
        Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>, linux-kernel@vger.kernel.org,
        vince@deater.net, eranian@google.com,
        Arnaldo Carvalho de Melo <acme@infradead.org>, tglx@linutronix.de
Subject: Re: [PATCH] perf/x86/intel/bts: don't dereference ds unconditionally
In-Reply-To: <20160920131220.xg5pbdjtznszuyzb@breakpoint.cc>
References: <20160906132353.19887-1-alexander.shishkin@linux.intel.com> <20160906132353.19887-5-alexander.shishkin@linux.intel.com> <20160920131220.xg5pbdjtznszuyzb@breakpoint.cc>
User-Agent: Notmuch/0.22.1 (http://notmuchmail.org) Emacs/24.5.1 (x86_64-pc-linux-gnu)
Date: Tue, 20 Sep 2016 16:44:43 +0300
Message-ID: <87r38eu1mc.fsf@ashishki-desk.ger.corp.intel.com>
MIME-Version: 1.0
Content-Type: text/plain
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

Sebastian Andrzej Siewior <sebastian@breakpoint.cc> writes:

> From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
>
> Since commit 4d4c47412464 ("perf/x86/intel/bts: Fix BTS PMI detection")
> my box goes boom on boot:
>
> | .... node  #0, CPUs:      #1 #2 #3 #4 #5 #6 #7
> | BUG: unable to handle kernel NULL pointer dereference at 0000000000000018
> | IP: [<ffffffff8100c463>] intel_bts_interrupt+0x43/0x130
> | Call Trace:
> |  <NMI> d [<ffffffff8100b341>] intel_pmu_handle_irq+0x51/0x4b0
> |  [<ffffffff81004d47>] perf_event_nmi_handler+0x27/0x40
>
> I don't know what is going on here but ds is not always dereferenced
> unconditionally hence here the `ds' check to avoid the crash.

Good catch! I'm going to guess you don't have the NMI watchdog enabled?

Thanks,
--
Alex