OTOH, there is no reason why we need to disable preemption over that
page_fault_disabled() region. There are code pathes which really do
not require to disable preemption for that.

We have that seperated in preempt-rt for obvious reasons and IIRC
Peter Zijlstra tried to distangle it in mainline some time ago. I
forgot why that never got merged.

Of course, we can completely separate that in our page fault code by doing
pagefault_disabled() checks instead of in_atomic() checks (even in add on
patches later).

We tie way too much stuff on the preemption count already, which is a
mightmare because we have no clear distinction of protection
scopes. 

Although it might not be optimal, but keeping a separate counter for
pagefault_disable() as part of the preemption counter seems to be the only
doable thing right now. I am not sure if a completely separated counter is even
possible, increasing the size of thread_info.

I am working on a prototype right now.

Thanks!

Thanks,

	tglx