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SubjectRe: [PATCH v5 5/5] cpuset: Rebuild root domain deadline accounting information
On 25/09/18 14:32, Peter Zijlstra wrote:
> On Mon, Sep 03, 2018 at 04:28:01PM +0200, Juri Lelli wrote:
> > +/*
> > + * Called with cpuset_mutex held (rebuild_sched_domains())
> > + * Called with hotplug lock held (rebuild_sched_domains_locked())
> > + * Called with sched_domains_mutex held (partition_and_rebuild_domains())
>
> Isn't that what we have lockdep_assert_held() for?

Indeed. I can put three of them inside the function, even though we have
a single path to here atm. Guess makes sense to protect any future change.

> > + */
> > +static void rebuild_root_domains(void)
> > +{
> > + struct cpuset *cs = NULL;
> > + struct cgroup_subsys_state *pos_css;
> > +
> > + rcu_read_lock();
> > +
> > + /*
> > + * Clear default root domain DL accounting, it will be computed again
> > + * if a task belongs to it.
> > + */
> > + dl_clear_root_domain(&def_root_domain);
> > +
> > + cpuset_for_each_descendant_pre(cs, pos_css, &top_cpuset) {
> > +
> > + if (cpumask_empty(cs->effective_cpus)) {
> > + pos_css = css_rightmost_descendant(pos_css);
> > + continue;
> > + }
> > +
> > + css_get(&cs->css);
> > +
> > + rcu_read_unlock();
>
> That looks really dodgy, but I suppose the comment near
> css_next_descendant_pre() spells out that this is in fact OK.

Plus update_cpumasks_hier() seems to do something similar. Maybe I
should switch to use css_tryget_online() as well?

Thanks,

- Juri

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