add_timer_on() isn't used by modules (in fact it's only used ONCE, in
workqueue.c) and it's not even a good api for drivers, in fact, the comment
for it says

 * This is not very scalable on SMP. Double adds are not possible.
Signed-off-by: Arjan van de Ven <arjan@infradead.org>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>