From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752640Ab0CTUpQ (ORCPT ); Sat, 20 Mar 2010 16:45:16 -0400 Received: from ogre.sisk.pl ([217.79.144.158]:57248 "EHLO ogre.sisk.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752172Ab0CTUpO (ORCPT ); Sat, 20 Mar 2010 16:45:14 -0400 From: "Rafael J. Wysocki" To: Linus Torvalds Subject: Re: [Regression, post-2.6.34-rc1][PATCH] x86 / perf: Fix suspend to RAM on HP nx6325 Date: Sat, 20 Mar 2010 21:48:01 +0100 User-Agent: KMail/1.12.4 (Linux/2.6.34-rc1-rjw; KDE/4.3.5; x86_64; ; ) Cc: Peter Zijlstra , pm list , LKML , Ingo Molnar , Andrew Morton References: <201003201507.15358.rjw@sisk.pl> <1269106609.9440.529.camel@laptop> In-Reply-To: MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <201003202148.01312.rjw@sisk.pl> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Saturday 20 March 2010, Linus Torvalds wrote: > > On Sat, 20 Mar 2010, Peter Zijlstra wrote: > > > > cpuhw = &per_cpu(cpu_hw_events, cpu); > > + if (!cpuhw) > > + return; > > How can an address-of expression be NULL? > > Yes, 'per_cpu()' is magic, but it shouldn't be possible to be _that_ > magic. It's rather against the whole C model. Yeah. A field in the object pointed to by it can be NULL, though. The appended patch fixes the breakage for me too. Rafael --- From: Rafael J. Wysocki Subject: x86 / perf: Fix suspend to RAM on HP nx6325 Commit 3f6da3905398826d85731247e7fbcf53400c18bd (perf: Rework and fix the arch CPU-hotplug hooks) broke suspend to RAM on my HP nx6325 (and most likely on other AMD-based boxes too) by allowing amd_pmu_cpu_offline() to be executed for CPUs that are going offline as part of the suspend process. The problem is that cpuhw->amd_nb may be NULL already when amd_pmu_cpu_offline() is called, so the function should make sure it's not NULL before accessing the object pointed to by it. Signed-off-by: Rafael J. Wysocki --- arch/x86/kernel/cpu/perf_event_amd.c | 4 ++++ 1 file changed, 4 insertions(+) Index: linux-2.6/arch/x86/kernel/cpu/perf_event_amd.c =================================================================== --- linux-2.6.orig/arch/x86/kernel/cpu/perf_event_amd.c +++ linux-2.6/arch/x86/kernel/cpu/perf_event_amd.c @@ -348,11 +348,15 @@ static void amd_pmu_cpu_offline(int cpu) raw_spin_lock(&amd_nb_lock); + if (!cpuhw->amd_nb) + goto unlock; + if (--cpuhw->amd_nb->refcnt == 0) kfree(cpuhw->amd_nb); cpuhw->amd_nb = NULL; + unlock: raw_spin_unlock(&amd_nb_lock); }