Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753538Ab0HZM6V (ORCPT ); Thu, 26 Aug 2010 08:58:21 -0400 Received: from casper.infradead.org ([85.118.1.10]:49148 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752502Ab0HZM6U convert rfc822-to-8bit (ORCPT ); Thu, 26 Aug 2010 08:58:20 -0400 Subject: Re: [PATCH] perf: fix possible divide-by-zero in perf_swevent_overflow() From: Peter Zijlstra To: DDD Cc: mingo@elte.hu, fweisbec@gmail.com, acme@redhat.com, paulus@samba.org, linux-kernel@vger.kernel.org In-Reply-To: <4C765FD3.9060904@windriver.com> References: <1282824438-13970-1-git-send-email-dongdong.deng@windriver.com> <1282824727.1975.747.camel@laptop> <4C765FD3.9060904@windriver.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT Date: Thu, 26 Aug 2010 14:58:06 +0200 Message-ID: <1282827486.1975.845.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.28.3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1817 Lines: 59 On Thu, 2010-08-26 at 20:36 +0800, DDD wrote: > Peter Zijlstra wrote: > > On Thu, 2010-08-26 at 20:07 +0800, Dongdong Deng wrote: > >> The event->hw.last_period is possible to zero, thus it will > >> cause divide_by_zero later in perf_swevent_set_period(). > > > > How can it be zero? > > When I am running the kgdbts to test the hw_breakpoint_layer with kgdb, > I get a call trace as following and this problem is hardly to reproduce. > > Maybe the root cause was from kgdb/hw_breakpoint_layer, Yeah, I think there's a bug in the hw_breakpoint stuff, does something like the below fix it? > but add a checking is good to us and harmless. :-) Except that code path is already too bloated and should be reduced not added to and conditionals are expensive. --- kernel/hw_breakpoint.c | 13 ++++++++++++- 1 files changed, 12 insertions(+), 1 deletions(-) diff --git a/kernel/hw_breakpoint.c b/kernel/hw_breakpoint.c index d71a987..f57ebee 100644 --- a/kernel/hw_breakpoint.c +++ b/kernel/hw_breakpoint.c @@ -600,9 +600,20 @@ static int __init init_hw_breakpoint(void) } core_initcall(init_hw_breakpoint); +static int hw_breakpoint_enable(struct perf_event *event) +{ + struct hw_perf_event *hwc = &event->hw; + + if (hwc->sample_period) { + hwc->last_period = hwc->sample_period; + perf_swevent_set_period(event); + } + + return arch_install_hw_breakpoint(event); +} struct pmu perf_ops_bp = { - .enable = arch_install_hw_breakpoint, + .enable = hw_breakpoint_enable, .disable = arch_uninstall_hw_breakpoint, .read = hw_breakpoint_pmu_read, }; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/