On (02/11/16 17:10), Petr Mladek wrote:
[..]
> > well, I believe it's ok. __rcu_read_lock() for CONFIG_PREEMPT_RCU
> > does current->rcu_read_lock_nesting++, so rcu_preempt_depth() works
> > as expected. otherwise, for !CONFIG_PREEMPT_RCU kernel,
> > __rcu_read_lock() does
> >
> > if (IS_ENABLED(CONFIG_PREEMPT_COUNT))
> > preempt_disable()
> >
> >
> > - if we run "CONFIG_PREEMPT_RCU" then rcu_preempt_depth()
> > works here.
> >
> > - if we run "!CONFIG_PREEMPT_RCU && CONFIG_PREEMPT_COUNT"
> > then preemptible() works for us
> >
> > - if we run "!CONFIG_PREEMPT_RCU && !CONFIG_PREEMPT_COUNT"
> > then preemptible() is always 0.
>
> I feel convinced. But we should somehow document it. I think how
> to do it effectively. I think that the following text would help
> me if I read it:
>
> /*
> * Safe context for rescheduling is detected only when
> * PREEMPT_COUNT is enabled. preemptible() always returns
> * false otherwise.
> *
> * RCU read sections must be detected separately. They
> * have a separate preemption counter when PREEMPT_RCU
> * is enabled.
> */
>
> I wanted to highlight why exactly the check returns 0 in !PREEMPT_COUNT
> kernel. I missed this a bit in you original comment. But feel free
> to change it as you like.
good point. thanks! will re-spin the patch set later today,
have no reliable internet connection at the moment.
-ss
