Re: [PATCH v3] pm_qos: make update_request callable from interrupt context

[mark gross <640e9920@gmail.com>]

On Mon, Jun 07, 2010 at 12:19:41PM -0400, James Bottomley wrote:
> On Mon, 2010-06-07 at 17:34 +0200, florian@mickler.org wrote:
> > We use the spinlocked notifier chain variant (struct
> > atomic_notifier_head) and add an __might_sleep() to the chain for
> > constraints which have non-atomic notifiers. This way we catch all
> > interrupt-context-update-sites at runtime.
> 
> Actually, I'm afraid we can't really call blocking notifiers through the
> atomic chain because we might end up with a contested chain call and a
> huge busy wait in the spinlock (especially if one of the notifiers is
> sleeping).
> 
> I think the pm_qos_object still needs the two notifier chains ... it's
> just that when set up, one must either fill an atomic or a blocking
> chain (leaving the other NULL).  We use the NULL to check to decide what
> chain to add notifiers to, and if the blocking chain is null, we refuse
> to add blocking notifiers (with a BUG). If the blocking chain is
> non-null, we register the might_sleep() notifier (actually, given the
> argument mismatch, you'll have to wrapper that).
> 
> James
Can't we just requiere that all notifier callbacks be atomic context
safe and not fart around with 2 classes of notifiers?

--mgross