Alexey Kuznetsov found some problems in the pi-futex code.

One of the root causes is:

When a wakeup happens, we do not to stop the chain walk so we
we follow a non existing locking chain.

Drop out when this happens.

Cc: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>