On Thu, Nov 27, 2014 at 09:03:01AM +0100, David Hildenbrand wrote:
> > 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.
> So we would have pagefault code rely on:
>
> in_disabled_pagefault() ( pagefault_disabled() ... whatever ) instead of
> in_atomic().
No, let's be more defensive: the page fault handler should do nothing if
in_atomic() just like now. But it could have a quick check and emit a one
time warning if page faults aren't disabled in addition.
That might help debugging but keeps the system more likely alive.
might_fault() however should call might_sleep() if page faults aren't
disabled, but that's what you proposed anyway I think.
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