From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753572Ab1CZS1X (ORCPT ); Sat, 26 Mar 2011 14:27:23 -0400 Received: from casper.infradead.org ([85.118.1.10]:38330 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753535Ab1CZS1V (ORCPT ); Sat, 26 Mar 2011 14:27:21 -0400 Subject: Re: [PATCH,RFC] perf: panic due to inclied cpu context task_ctx value From: Peter Zijlstra To: Oleg Nesterov Cc: Jiri Olsa , Paul Mackerras , Ingo Molnar , linux-kernel@vger.kernel.org In-Reply-To: <20110326173545.GA22919@redhat.com> References: <20110324164436.GC1930@jolsa.brq.redhat.com> <1301153868.2250.359.camel@laptop> <20110326161346.GA18272@redhat.com> <1301157483.2250.366.camel@laptop> <20110326170922.GA20329@redhat.com> <20110326173545.GA22919@redhat.com> Content-Type: text/plain; charset="UTF-8" Date: Sat, 26 Mar 2011 19:29:28 +0100 Message-ID: <1301164168.2250.370.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 2011-03-26 at 18:35 +0100, Oleg Nesterov wrote: > On 03/26, Oleg Nesterov wrote: > > > > On 03/26, Peter Zijlstra wrote: > > > > > > diff --git a/kernel/perf_event.c b/kernel/perf_event.c > > > index c75925c..e9e4e35 100644 > > > --- a/kernel/perf_event.c > > > +++ b/kernel/perf_event.c > > > @@ -1073,6 +1073,8 @@ event_sched_out(struct perf_event *event, > > > if (!is_software_event(event)) > > > cpuctx->active_oncpu--; > > > ctx->nr_active--; > > > + if (!ctx->nr_active && cpuctx->task_ctx == ctx) > > > + cpuctx->task_ctx = NULL; > > > > If we clear cpuctx->task_ctx, we should also clear ctx->is_active. Right. > > Otherwise I can't see any problem, but I do not understand this code > > enough. > > but probably we also need update_context_time(). It looks like event_sched_out() relies on up-to-date ctx->time through perf_event_time() and most call-paths leading to event_sched_out() do indeed seem to update the ctx time, all except the move_group branch in perf_event_open() afaict. Sadly the reproducer doesn't seem to trigger the issue at all, its still running on a plain -tip kernel.