From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751029AbeBIKLr (ORCPT ); Fri, 9 Feb 2018 05:11:47 -0500 Received: from merlin.infradead.org ([205.233.59.134]:52662 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750895AbeBIKLp (ORCPT ); Fri, 9 Feb 2018 05:11:45 -0500 Date: Fri, 9 Feb 2018 11:11:28 +0100 From: Peter Zijlstra To: linxiulei@gmail.com Cc: jolsa@redhat.com, mingo@redhat.com, acme@kernel.org, alexander.shishkin@linux.intel.com, tglx@linutronix.de, eranian@gmail.com, torvalds@linux-foundation.org, brendan.d.gregg@gmail.com, linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, yang_oliver@hotmail.com, jinli.zjl@alibaba-inc.com, "leilei.lin" Subject: Re: [PATCH RESEND v4] perf/core: Fix installing cgroup event into cpu Message-ID: <20180209101128.GF25181@hirez.programming.kicks-ass.net> References: <20180208033344.71933-1-linxiulei@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180208033344.71933-1-linxiulei@gmail.com> User-Agent: Mutt/1.9.2 (2017-12-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Feb 08, 2018 at 11:33:44AM +0800, linxiulei@gmail.com wrote: > From: "leilei.lin" > > Do not install cgroup event into the CPU context and schedule it > if the cgroup is not running on this CPU > > While there is no task of cgroup running specified CPU, current > kernel still install cgroup event into CPU context that causes > another cgroup event can't be installed into this CPU. > > This patch prevent scheduling events at __perf_install_in_context() > and installing events at list_update_cgroup_event() if cgroup isn't > running on specified CPU. > > Signed-off-by: leilei.lin > --- > v2: Set cpuctx->cgrp only if the same cgroup is running on this > CPU otherwise following events couldn't be activated immediately > v3: Enhance the comments and commit message > v4: Adjust to config > > kernel/events/core.c | 50 +++++++++++++++++++++++++++++++++++++------------- > 1 file changed, 37 insertions(+), 13 deletions(-) > > diff --git a/kernel/events/core.c b/kernel/events/core.c > index 4df5b69..fd28d61 100644 > --- a/kernel/events/core.c > +++ b/kernel/events/core.c > @@ -933,31 +933,41 @@ list_update_cgroup_event(struct perf_event *event, > { > struct perf_cpu_context *cpuctx; > struct list_head *cpuctx_entry; > + struct perf_cgroup *cgrp; > > if (!is_cgroup_event(event)) > return; > > /* > * Because cgroup events are always per-cpu events, > * this will always be called from the right CPU. > */ > cpuctx = __get_cpu_context(ctx); > + cgrp = perf_cgroup_from_task(current, ctx); > > + /* > + * if only the cgroup is running on this cpu, > + * we put/remove this cgroup into cpu context. > + * Or it would case mismatch in following cgroup > + * events at event_filter_match() > + */ > + if (cgroup_is_descendant(cgrp->css.cgroup, event->cgrp->css.cgroup)) { > + if (add) > cpuctx->cgrp = cgrp; > + else > + cpuctx->cgrp = NULL; > } I am still not convinced this is correct. Suppose we have R / \ A B / \ C And our current task is of B, and B has an event. We then install an event in C, if we then destroy our event in C, it would clear cpuctx->cgrp, which is wrong, since there is still an event in B. Simpler still, if B were to have 2 events, and we'd remove one, that would still clear cpuctx->cgrp, even though there is an event left. This is the exact issue I pointed out last time, and I still don't see how it would now be correct. Northing explains why its ok to have NULL cpuctx->cgrp when there are in fact still cgroup events on the CPU.