Since the tasklist is protected by rcu list operations, it is safe
to convert the read_lock()s to rcu_read_lock().
Suggested-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: NMandeep Singh Baines <msb@google.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>