Re: PATCH? hrtimer_wakeup: fix a theoretical race wrt rt_mutex_slowlock()

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

> Yes. On x86 (and x86-64) you'll never see this, because writes are always 
> seen in order regardless, and in addition, the spin_lock is actually 
> totally serializing anyway. On most other architectures, the spin_lock 
> will serialize all the writes too, but it's not guaranteed, so in theory 
> you're right. I suspect no actual architecture will do this, but hey, 
> when talking memory ordering, safe is a lot better than sorry.

PowerPC doesn't serialize the writes on spin_lock, only on spin_unlock.

(That is, previous writes can "leak" into the lock, but writes done
before the unlock can't leak out of the spinlock).

Now, I've just glanced at the thread, so I don't know if that's relevant
to the problems you guys are talking about :-)

Ben.