From cdacbe1f91264687af956e810278030f2ab5a3d0 Mon Sep 17 00:00:00 2001
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Date: Sat, 11 Jul 2015 16:24:45 -0700
Subject: [PATCH] rcu: Add fastpath bypassing funnel locking

In the common case, there will be only one expedited grace period in
the system at a given time, in which case it is not helpful to use
funnel locking.  This commit therefore adds a fastpath that bypasses
funnel locking when the root ->exp_funnel_mutex is not held.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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