From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752098AbcITNyd (ORCPT ); Tue, 20 Sep 2016 09:54:33 -0400 Received: from mga07.intel.com ([134.134.136.100]:37703 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751443AbcITNya (ORCPT ); Tue, 20 Sep 2016 09:54:30 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.30,368,1470726000"; d="scan'208";a="1059503754" From: Alexander Shishkin To: Sebastian Andrzej Siewior , Ingo Molnar Cc: Peter Zijlstra , linux-kernel@vger.kernel.org, vince@deater.net, eranian@google.com, Arnaldo Carvalho de Melo , tglx@linutronix.de Subject: Re: [PATCH] perf/x86/intel/bts: don't dereference ds unconditionally In-Reply-To: <87r38eu1mc.fsf@ashishki-desk.ger.corp.intel.com> References: <20160906132353.19887-1-alexander.shishkin@linux.intel.com> <20160906132353.19887-5-alexander.shishkin@linux.intel.com> <20160920131220.xg5pbdjtznszuyzb@breakpoint.cc> <87r38eu1mc.fsf@ashishki-desk.ger.corp.intel.com> User-Agent: Notmuch/0.22.1 (http://notmuchmail.org) Emacs/24.5.1 (x86_64-pc-linux-gnu) Date: Tue, 20 Sep 2016 16:54:26 +0300 Message-ID: <87oa3iu165.fsf@ashishki-desk.ger.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Alexander Shishkin writes: > Sebastian Andrzej Siewior writes: > >> From: Sebastian Andrzej Siewior >> >> 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: [] intel_bts_interrupt+0x43/0x130 >> | Call Trace: >> | d [] intel_pmu_handle_irq+0x51/0x4b0 >> | [] 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? That is to say, Reviewed-by: Alexander Shishkin