Re: [PATCH RFC 01/15] uaccess: count pagefault_disable() levels in pagefault_disabled

[Peter Zijlstra]

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.
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