rcu: Avoid redundant grace-period kthread wakeups

When setting up an in-the-future "advanced" grace period, the code needs
to wake up the relevant grace-period kthread, which it currently does
unconditionally.  However, this results in needless wakeups in the case
where the advanced grace period is being set up by the grace-period
kthread itself, which is a non-uncommon situation.  This commit therefore
checks to see if the running thread is the grace-period kthread, and
avoids doing the irq_work_queue()-mediated wakeup in that case.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Git-commit: 1eafd31c640d6799c63136246a59d608bed93c74
[kishank@codeaurora.org resolve trivial conflicts]
Signed-off-by: Kishan Kumar <kishank@codeaurora.org>