xtensa: Add missing RCU idle APIs on idle loop

xtensa: Add missing RCU idle APIs on idle loop

Commit-ID:  11ad47a0edbd62bfc0547cfcdf227a911433f207
Gitweb:     http://git.kernel.org/tip/11ad47a0edbd62bfc0547cfcdf227a911433f207
Author:     Frederic Weisbecker <fweisbec@gmail.com>
AuthorDate: Wed, 22 Aug 2012 17:27:34 +0200
Committer:  Paul E. McKenney <paulmck@linux.vnet.ibm.com>
CommitDate: Sun, 23 Sep 2012 07:44:51 -0700

xtensa: Add missing RCU idle APIs on idle loop

In the old times, the whole idle task was considered
as an RCU quiescent state. But as RCU became more and
more successful overtime, some RCU read side critical
section have been added even in the code of some
architectures idle tasks, for tracing for example.

So nowadays, rcu_idle_enter() and rcu_idle_exit() must
be called by the architecture to tell RCU about the part
in the idle loop that doesn't make use of rcu read side
critical sections, typically the part that puts the CPU
in low power mode.

This is necessary for RCU to find the quiescent states in
idle in order to complete grace periods.

Add this missing pair of calls in the xtensa's idle loop.

Reported-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: <stable@vger.kernel.org> # 3.3+
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Chris Zankel <chris@zankel.net>