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SubjectRe: [PATCH v14 1/6] sched/core: uclamp: Extend CPU's cgroup controller
On Mon, Sep 02, 2019 at 04:02:57PM -0700, Suren Baghdasaryan <surenb@google.com> wrote:
> > +static inline void cpu_uclamp_print(struct seq_file *sf,
> > + enum uclamp_id clamp_id)
> > [...]
> > + rcu_read_lock();
> > + tg = css_tg(seq_css(sf));
> > + util_clamp = tg->uclamp_req[clamp_id].value;
> > + rcu_read_unlock();
> > +
> > + if (util_clamp == SCHED_CAPACITY_SCALE) {
> > + seq_puts(sf, "max\n");
> > + return;
> > + }
> > +
> > + percent = tg->uclamp_pct[clamp_id];
>
> 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.

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