On Wed, Jan 07, 2009 at 12:55:49PM -0800, Linus Torvalds wrote:

	void loop_while_oncpu(struct mutex *lock, struct thread_struct *thread)
	{
		for (;;) {
			unsigned cpu;
			struct runqueue *rq;

			if (lock->owner != thread)
				break;

			/*
			 * Need to access the cpu field knowing that
			 * DEBUG_PAGEALLOC could have unmapped it if
			 * the mutex owner just released it and exited.
			 */
			if (__get_user(cpu, &thread->cpu))
				break;

I appreciate this is sample code, but using __get_user() on
non-userspace pointers messes up architectures which have separate
user/kernel spaces (eg the old 4G/4G split for x86-32).  Do we have an
appropriate function for kernel space pointers?  Is this a good reason
to add one?

-- 
Matthew Wilcox				Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."