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SubjectRe: [RFC 0/2] Reenable might_sleep() checks for might_fault() when atomic
> 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.

Sounds sane if we increase both counters!

>
> might_fault() however should call might_sleep() if page faults aren't
> disabled, but that's what you proposed anyway I think.

Jap, sounds good to me. Will see if I can come up with something.

Thanks!



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