Messages in this thread | | | Date | Thu, 27 Nov 2014 13:04:41 +0100 | From | Heiko Carstens <> | Subject | Re: [RFC 0/2] Reenable might_sleep() checks for might_fault() when atomic |
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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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