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

[Peter Zijlstra]

On Wed, May 06, 2015 at 07:50:25PM +0200, David Hildenbrand wrote:
> +/*
> + * Is the pagefault handler disabled? If so, user access methods will not sleep.
> + */
> +#define pagefault_disabled() (current->pagefault_disabled != 0)

So -RT has:

static inline bool pagefault_disabled(void)
{
	return current->pagefault_disabled || in_atomic();
}

AFAICR we did this to avoid having to do both:

	preempt_disable();
	pagefault_disable();

in a fair number of places -- just like this patch-set does, this is
touching two cachelines where one would have been enough.

Also, removing in_atomic() from fault handlers like you did
significantly changes semantics for interrupts (soft, hard and NMI).

So while I agree with most of these patches, I'm very hesitant on the
above little detail.
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