smp_call_function_single() can deadlock if the caller disabled local
interrupts (the target CPU could be spinning on call_lock).  Check for that.

Why on earth do these functions use spin_lock_bh()??

Cc: "Randy.Dunlap" <rdunlap@xenotime.net>
Cc: Andi Kleen <ak@suse.de>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>