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Date:   Mon, 4 Nov 2019 19:57:42 +0100
From:   Michal =?iso-8859-1?Q?Koutn=FD?= <mkoutny@suse.com>
To:     Juri Lelli <juri.lelli@redhat.com>, mathieu.poirier@linaro.org
Cc:     peterz@infradead.org, mingo@redhat.com, rostedt@goodmis.org,
        tj@kernel.org, linux-kernel@vger.kernel.org,
        luca.abeni@santannapisa.it, claudio@evidence.eu.com,
        tommaso.cucinotta@santannapisa.it, bristot@redhat.com,
        lizefan@huawei.com, longman@redhat.com, dietmar.eggemann@arm.com,
        cgroups@vger.kernel.org
Subject: Re: [PATCH v9 3/8] cpuset: Rebuild root domain deadline accounting
 information
Message-ID: <20191104185742.GC7827@blackbody.suse.cz>
References: <20190719140000.31694-1-juri.lelli@redhat.com>
 <20190719140000.31694-4-juri.lelli@redhat.com>
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Hello.

I came across a cgroup_enable_task_cg_lists() call from the cpuset
controller...

On Fri, Jul 19, 2019 at 03:59:55PM +0200, Juri Lelli <juri.lelli@redhat.com> wrote:
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> [...]
> +static void rebuild_root_domains(void)
> +{
> +	struct cpuset *cs = NULL;
> +	struct cgroup_subsys_state *pos_css;
> +
> +	lockdep_assert_held(&cpuset_mutex);
> +	lockdep_assert_cpus_held();
> +	lockdep_assert_held(&sched_domains_mutex);
> +
> +	cgroup_enable_task_cg_lists();
...and I wonder why is it necessary to call at this place?

(IIUC, before cpuset hierarchy is anywhere mounted it's mere top_cpuset,
i.e. processing the top_cpuset alone is enough. And if anyone wants to
create any non-root cpusets, they have to mount the hierachy first, i.e.
no need to call cgroup_enable_task_cg_lists() manually. Also if I'm not
overlooking anything, the race between hotplug and mount (more precisely
new cpuset creation) should be synchronized by cpuset_mutex.)

Thanks,
Michal

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