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From: Namhyung Kim <namhyung@kernel.org>
To: Chengming Zhou <zhouchengming@bytedance.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Jiri Olsa <jolsa@kernel.org>,
	Stephane Eranian <eranian@google.com>,
	linux-perf-users <linux-perf-users@vger.kernel.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	duanxiongchun@bytedance.com, songmuchun@bytedance.com
Subject: Re: [External] Re: [PATCH v2 1/6] perf/core: Fix incosistency between cgroup sched_out and sched_in
Date: Tue, 22 Mar 2022 15:06:39 -0700	[thread overview]
Message-ID: <CAM9d7chL6r=4Ay6udSv-heyH3pAdH=Cp+2mXU2-+Z7yHt+aH7w@mail.gmail.com> (raw)
In-Reply-To: <1c9f2383-ec9f-f819-d7be-23aed2bf121a@bytedance.com>

Hello,

On Tue, Mar 22, 2022 at 8:28 AM Chengming Zhou
<zhouchengming@bytedance.com> wrote:
>
> On 2022/3/22 11:16 下午, Chengming Zhou wrote:
> > Hi peter,
> >
> > On 2022/3/22 10:54 下午, Peter Zijlstra wrote:
> >> On Tue, Mar 22, 2022 at 09:38:21PM +0800, Chengming Zhou wrote:
> >>> On 2022/3/22 8:59 下午, Peter Zijlstra wrote:
> >>>> On Tue, Mar 22, 2022 at 08:08:29PM +0800, Chengming Zhou wrote:
> >>>>> There is a race problem that can trigger WARN_ON_ONCE(cpuctx->cgrp)
> >>>>> in perf_cgroup_switch().
> >>>>>
> >>>>> CPU1                                      CPU2
> >>>>> (in context_switch)                       (attach running task)
> >>>>> perf_cgroup_sched_out(prev, next)
> >>>>>   cgrp1 == cgrp2 is True
> >>>>>                                   next->cgroups = cgrp3
> >>>>>                                   perf_cgroup_attach()
> >>>>> perf_cgroup_sched_in(prev, next)
> >>>>>   cgrp1 == cgrp3 is False
>
> I see, you must have been misled by my wrong drawing above ;-)
> I'm sorry, perf_cgroup_attach() on the right should be put at the bottom.
>
> CPU1                                            CPU2
> (in context_switch)                             (attach running task)
> perf_cgroup_sched_out(prev, next)
>         cgrp1 == cgrp2 is True
>                                                 next->cgroups = cgrp3
> perf_cgroup_sched_in(prev, next)
>         cgrp1 == cgrp3 is False
>                                                 __perf_cgroup_move()
>

Yep, this is a real race and I saw the warnings reported sometimes.
The perf_cgroup_attach() is called after the task's cgroup is changed.

Thanks,
Namhyung

  reply	other threads:[~2022-03-22 22:07 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-03-22 12:08 [PATCH v2 0/6] perf/core: Fixes and cleanup for cgroup events Chengming Zhou
2022-03-22 12:08 ` [PATCH v2 1/6] perf/core: Fix incosistency between cgroup sched_out and sched_in Chengming Zhou
2022-03-22 12:59   ` Peter Zijlstra
2022-03-22 13:38     ` [External] " Chengming Zhou
2022-03-22 14:54       ` Peter Zijlstra
2022-03-22 15:16         ` Chengming Zhou
2022-03-22 15:28           ` Chengming Zhou
2022-03-22 22:06             ` Namhyung Kim [this message]
2022-03-23  8:11             ` Peter Zijlstra
2022-03-22 12:08 ` [PATCH v2 2/6] perf/core: Introduce percpu perf_cgroup Chengming Zhou
2022-03-22 13:01   ` Peter Zijlstra
2022-03-22 16:33     ` [External] " Chengming Zhou
2022-03-23  8:13       ` Peter Zijlstra
2022-03-23 12:58         ` Chengming Zhou
2022-03-22 22:21     ` Namhyung Kim
2022-03-22 22:18   ` Namhyung Kim
2022-03-23  1:27     ` [Phishing Risk] [External] " Chengming Zhou
2022-03-23 12:51   ` Peter Zijlstra
2022-03-23 13:07     ` [External] " Chengming Zhou
2022-03-23 13:17       ` Peter Zijlstra
2022-03-23 13:37         ` Chengming Zhou
2022-03-23 14:05           ` Peter Zijlstra
2022-03-23 15:44             ` Chengming Zhou
2022-03-22 12:08 ` [PATCH v2 3/6] perf/core: Don't pass task around when ctx sched in Chengming Zhou
2022-03-22 13:01   ` Peter Zijlstra
2022-03-22 12:08 ` [PATCH v2 4/6] perf/core: Use stable cpuctx->cgrp when update perf cgroup time Chengming Zhou
2022-03-22 13:03   ` Peter Zijlstra
2022-03-22 12:08 ` [PATCH v2 5/6] perf/core: Always set cpuctx cgrp when enable cgroup event Chengming Zhou
2022-03-22 12:08 ` [PATCH v2 6/6] perf/core: Don't need event_filter_match when merge_sched_in() Chengming Zhou

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