Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Tue, 3 Sep 2019 10:52:48 +0200
From:   Michal =?iso-8859-1?Q?Koutn=FD?= <mkoutny@suse.com>
To:     Suren Baghdasaryan <surenb@google.com>
Cc:     Patrick Bellasi <patrick.bellasi@arm.com>,
        Alessio Balsini <balsini@android.com>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Morten Rasmussen <morten.rasmussen@arm.com>,
        Quentin Perret <quentin.perret@arm.com>,
        Joel Fernandes <joelaf@google.com>,
        Paul Turner <pjt@google.com>,
        Steve Muckle <smuckle@google.com>,
        Todd Kjos <tkjos@google.com>,
        Peter Zijlstra <peterz@infradead.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
        Tejun Heo <tj@kernel.org>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Ingo Molnar <mingo@redhat.com>,
        cgroups mailinglist <cgroups@vger.kernel.org>,
        linux-api@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
        linux-pm@vger.kernel.org
Subject: Re: [PATCH v14 1/6] sched/core: uclamp: Extend CPU's cgroup
 controller
Message-ID: <20190903085248.GB8756@blackbody.suse.cz>
References: <20190822132811.31294-1-patrick.bellasi@arm.com>
 <20190822132811.31294-2-patrick.bellasi@arm.com>
 <CAJuCfpGWtrg02LNE3PJZag9-LLVT=by2v+9x_tm1PyoXwZ8DqQ@mail.gmail.com>
MIME-Version: 1.0
Content-Type: multipart/signed; micalg=pgp-sha256;
        protocol="application/pgp-signature"; boundary="VrqPEDrXMn8OVzN4"
Content-Disposition: inline
In-Reply-To: <CAJuCfpGWtrg02LNE3PJZag9-LLVT=by2v+9x_tm1PyoXwZ8DqQ@mail.gmail.com>
User-Agent: Mutt/1.10.1 (2018-07-13)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


--VrqPEDrXMn8OVzN4
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
Content-Transfer-Encoding: quoted-printable

On Mon, Sep 02, 2019 at 04:02:57PM -0700, Suren Baghdasaryan <surenb@google=
=2Ecom> wrote:
> > +static inline void cpu_uclamp_print(struct seq_file *sf,
> > +                                   enum uclamp_id clamp_id)
> > [...]
> > +       rcu_read_lock();
> > +       tg =3D css_tg(seq_css(sf));
> > +       util_clamp =3D tg->uclamp_req[clamp_id].value;
> > +       rcu_read_unlock();
> > +
> > +       if (util_clamp =3D=3D SCHED_CAPACITY_SCALE) {
> > +               seq_puts(sf, "max\n");
> > +               return;
> > +       }
> > +
> > +       percent =3D tg->uclamp_pct[clamp_id];
>=20
> You are taking RCU lock when accessing tg->uclamp_req but not when
> accessing tg->uclamp_pct.
Good point.

> Is that intentional? Can tg be destroyed under you?
Actually, the rcu_read{,un}lock should be unnecessary in the context of
the kernfs file op handler -- the tg/css won't go away as long as its
kernfs file is being worked with.


--VrqPEDrXMn8OVzN4
Content-Type: application/pgp-signature; name="signature.asc"
Content-Description: Digital signature

-----BEGIN PGP SIGNATURE-----
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=B4jM
-----END PGP SIGNATURE-----

--VrqPEDrXMn8OVzN4--