From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751558AbZKZRhD (ORCPT ); Thu, 26 Nov 2009 12:37:03 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750938AbZKZRhD (ORCPT ); Thu, 26 Nov 2009 12:37:03 -0500 Received: from casper.infradead.org ([85.118.1.10]:47974 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750872AbZKZRhC (ORCPT ); Thu, 26 Nov 2009 12:37:02 -0500 Subject: Re: [PATCH] perf_events: fix read() bogus counts when in error state From: Peter Zijlstra To: Stephane Eranian Cc: linux-kernel@vger.kernel.org, mingo@elte.hu, paulus@samba.org, perfmon2-devel@lists.sourceforge.net, eranian@gmail.com In-Reply-To: <4b0eb9ce.0508d00a.573b.ffffeab6@mx.google.com> References: <4b0eb9ce.0508d00a.573b.ffffeab6@mx.google.com> Content-Type: text/plain; charset="UTF-8" Date: Thu, 26 Nov 2009 18:36:56 +0100 Message-ID: <1259257016.31676.308.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.28.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2009-11-26 at 09:24 -0800, Stephane Eranian wrote: > When a pinned group cannot be scheduled it goes into error state. > Normally a group cannot go out of error state without being explicitly > re-enabled or disabled. There was a bug in per-thread mode, whereby > upon termination of the thread, the group would transition from error > to off leading to bogus counts and timing information returned by > read(). > Signed-off-by: Stephane Eranian Right, good catch, totally forgot about error state :/ Acked-by: Peter Zijlstra > --- > perf_event.c | 11 ++++++++++- > 1 file changed, 10 insertions(+), 1 deletion(-) > > diff --git a/kernel/perf_event.c b/kernel/perf_event.c > index 0b0d5f7..7a8bb5b 100644 > --- a/kernel/perf_event.c > +++ b/kernel/perf_event.c > @@ -333,7 +333,16 @@ list_del_event(struct perf_event *event, struct perf_event_context *ctx) > event->group_leader->nr_siblings--; > > update_event_times(event); > - event->state = PERF_EVENT_STATE_OFF; > + > + /* > + * If event was in error state, then keep it > + * that way, otherwise bogus counts will be > + * returned on read(). The only way to get out > + * of error state is by explicit re-enabling > + * of the event > + */ > + if (event->state > PERF_EVENT_STATE_OFF) > + event->state = PERF_EVENT_STATE_OFF; > > /* > * If this was a group event with sibling events then