Messages in this thread | | | From | Joel Fernandes <> | Date | Tue, 3 Sep 2019 10:21:59 -0400 | Subject | Re: [PATCH v14 1/6] sched/core: uclamp: Extend CPU's cgroup controller |
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On Tue, Sep 3, 2019 at 4:53 AM Michal Koutný <mkoutny@suse.com> wrote: > > 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. >
Also, add to that the fact that there is no rcu_dereference() call to access any of the pointers in the reader or any of its callers. And, I don't see any "wait for completion" type of pattern here so that rcu_read_{lock, unlock}() pair does seem useless.
thanks,
- Joel
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