linux-kernel - Re: [PATCH v11 3/5] sched/core: uclamp: Propagate system defaults to root group

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Message-ID: <20190716153610.GE32540@blackbody.suse.cz>
Date:   Tue, 16 Jul 2019 17:36:10 +0200
From:   Michal Koutný <mkoutny@...e.com>
To:     Patrick Bellasi <patrick.bellasi@....com>
Cc:     Alessio Balsini <balsini@...roid.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Quentin Perret <quentin.perret@....com>,
        Joel Fernandes <joelaf@...gle.com>,
        Paul Turner <pjt@...gle.com>,
        Steve Muckle <smuckle@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Todd Kjos <tkjos@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Tejun Heo <tj@...nel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org
Subject: Re: [PATCH v11 3/5] sched/core: uclamp: Propagate system defaults to
 root group

On Tue, Jul 16, 2019 at 03:34:17PM +0100, Patrick Bellasi <patrick.bellasi@....com> wrote:
> > cpu_util_update_eff internally calls css_for_each_descendant_pre() so
> > this should be protected with rcu_read_lock().
> 
> Right, good catch! Will add in v12.
When I responded to your other patch, it occurred to me that since
cpu_util_update_eff goes writing down to child csses, it should take
also uclamp_mutex here to avoid race with direct cgroup attribute
writers.