Messages in this thread | | | Date | Thu, 7 May 2015 13:40:30 +0200 | From | David Hildenbrand <> | Subject | Re: [PATCH RFC 01/15] uaccess: count pagefault_disable() levels in pagefault_disabled |
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> On Thu, May 07, 2015 at 12:50:53PM +0200, David Hildenbrand wrote: > > Just to make sure we have a common understanding (as written in my cover > > letter): > > > > Your suggestion won't work with !CONFIG_PREEMPT (!CONFIG_PREEMPT_COUNT). If > > there is no preempt counter, in_atomic() won't work. > > But there is, we _always_ have a preempt_count, and irq_enter() et al. > _always_ increment the relevant bits. > > The thread_info::preempt_count field it never under PREEMPT_COUNT > include/asm-generic/preempt.h provides stuff regardless of > PREEMPT_COUNT. > > See how __irq_enter() -> preempt_count_add(HARDIRQ_OFFSET) -> > __preempt_count_add() _always_ just works.
Okay thinking about this further, I think I got your point. That basically means that the in_atomic() check makes sense for irqs.
But in my opinion, it does not help do replace
preempt_disable() pagefault_disable()
by
preempt_disable()
(as discussed because of the PREEMPT_COUNT stuff)
So I agree that we should better add it to not mess with hard/soft irq.
> > Its only things like preempt_disable() / preempt_enable() that get > munged depending on PREEMPT_COUNT/PREEMPT. >
But anyhow, opinions seem to differ how to best handle that whole stuff.
I think a separate counter just makes sense, as we are dealing with two different concepts and we don't want to lose the preempt_disable =^ NOP for !CONFIG_PREEMPT.
I also think that
pagefault_disable() rt = copy_from_user() pagefault_enable()
is a valid use case.
So any suggestions how to continue?
Thanks!
David
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