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    SubjectRe: [PATCH RFC 01/15] uaccess: count pagefault_disable() levels in pagefault_disabled
    > 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.
    >
    > Its only things like preempt_disable() / preempt_enable() that get
    > munged depending on PREEMPT_COUNT/PREEMPT.
    >

    Sorry for the confusion. Sure, there is always the count.

    My point is that preempt_disable() won't result in an in_atomic() == true
    with !PREEMPT_COUNT, so I don't see any point in adding in to the pagefault
    handlers. It is not reliable.


    David



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