On Thu, 2012-04-26 at 16:59 -0700, Andrew Morton wrote:
> > +void clear_tasks_mm_cpumask(int cpu)
>
> The operation of this function was presumably obvious to you at the
> time you wrote it, but that isn't true of other people at later times.
>
> Please document it?
>
>
> > +{
> > + struct task_struct *p;
> > +
> > + /*
> > + * This function is called after the cpu is taken down and marked
> > + * offline,
>
> hm, well. Who said that this function will only ever be called
> after that CPU was taken down? There is nothing in the function name
> nor in the (absent) documentation which enforces this precondition.
>
> If someone tries to use this function for a different purpose, or
> copies-and-modifies it for a different purpose, we just shot them in
> the foot.
>
> They'd be pretty dumb to do that without reading the local comment,
> but still...
Methinks something simple like:
WARN_ON(cpu_online(cpu));
Ought to cure that worry, no? :-)
>
> > so its not like new tasks will ever get this cpu set in
> > + * their mm mask. -- Peter Zijlstra
> > + * Thus, we may use rcu_read_lock() here, instead of grabbing
> > + * full-fledged tasklist_lock.
> > + */
> > + rcu_read_lock();
> > + for_each_process(p) {
> > + struct task_struct *t;
> > +
> > + t = find_lock_task_mm(p);
> > + if (!t)
> > + continue;
> > + cpumask_clear_cpu(cpu, mm_cpumask(t->mm));
> > + task_unlock(t);
> > + }
> > + rcu_read_unlock();
> > +}
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