Avoid a deadlock during panic.  Don't take the smp_call_function lock in
smp_send_stop()

Also fix the documentation to conform to Linux standards.
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>