Il 17/05/2013 06:36, liu ping fan ha scritto:
>> > + /* Mark the writer thread offline to make sure we don't wait for
>> > + * our own quiescent state. This allows using synchronize_rcu()
>> > + * in threads registered as readers.
>> > + *
>> > + * rcu_thread_offline() and rcu_thread_online() include a
>> > + * memory barrier.
>> > + */
>> > + if (was_online) {
>> > + rcu_thread_offline();
> Encourage the user to call synchronize_rcu() in reader?
Not in a read-side critical section, but in a *thread registered as
reader*. And in QEMU, all threads actually are registered as readers.
> I think the caller should ensure it is outside read-section.
That would be possible by adding a small overhead to rcu_read_lock/unlock.
> Also online can be
> nested which make the situation even worse.
It's not online that can be nested, only offline. So:
- if the thread is already marked as offline, there will be no effect.
- if the thread is not marked as offline, it will be.
Paolo
