On Thu, 27 Nov 2014, Heiko Carstens wrote:

On Thu, Nov 27, 2014 at 09:03:01AM +0100, David Hildenbrand wrote:

quoted

quoted

Code like
	spin_lock(&lock);
	if (copy_to_user(...))
		rc = ...
	spin_unlock(&lock);
really *should* generate warnings like it did before.

And *only* code like
	spin_lock(&lock);

Is only code like this valid or also with the spin_lock() dropped?
(e.g. the access in patch1 if I remember correctly)

So should page_fault_disable() increment the pagefault counter and the preempt
counter or only the first one?

Given that a sequence like

	page_fault_disable();
 	if (copy_to_user(...))
 		rc = ...
 	page_fault_enable();

is correct code right now I think page_fault_disable() should increase both.
No need for surprising semantic changes.

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.

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

Thanks,

	tglx