rcu: Add "notrace" to RCU function headers used by ftrace

Both rcu_read_lock_sched_notrace() and
rcu_read_unlock_sched_notrace() are used by ftrace, and thus
need to be marked "notrace".

Unfortunately, my naive assumption that gcc would see the inner
"notrace" does not hold.

Kudos to Lai Jiangshan for noting this.

Reported-by: Ingo Molnar <mingo@elte.hu>
Bug-spotted-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: akpm@linux-foundation.org
Cc: mathieu.desnoyers@polymtl.ca
Cc: josht@linux.vnet.ibm.com
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
LKML-Reference: <12511321213243-git-send-email->
Signed-off-by: Ingo Molnar <mingo@elte.hu>