On 12/06, Srivatsa S. Bhat wrote:
>
> +void get_online_cpus_atomic(void)
> +{
> + int c, old;
> +
> + preempt_disable();
> + read_lock(&hotplug_rwlock);
Confused... Why it also takes hotplug_rwlock?
> +
> + for (;;) {
> + c = atomic_read(&__get_cpu_var(atomic_reader_refcount));
> + if (unlikely(writer_active(c))) {
> + cpu_relax();
> + continue;
> + }
> +
> + old = atomic_cmpxchg(&__get_cpu_var(atomic_reader_refcount),
> + c, c + 1);
> +
> + if (likely(old == c))
> + break;
> +
> + c = old;
> + }
> +}
while (!atomic_inc_unless_negative(...))
cpu_relax();
and atomic_dec_unless_positive() in disable_atomic_reader().
Obviously you can't use get_online_cpus_atomic() under rq->lock or
task->pi_lock or any other lock CPU_DYING can take. Probably this is
fine, but perhaps it makes sense to add the lockdep annotations.
Oleg.
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