rcu: Push lock release to rcu_start_gp()'s callers

If CPUs are to give prior notice of needed grace periods, it will be
necessary to invoke rcu_start_gp() without dropping the root rcu_node
structure's ->lock.  This commit takes a second step in this direction
by moving the release of this lock to rcu_start_gp()'s callers.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index df50502..073ded2 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -2174,7 +2174,6 @@
 	unsigned long c;
 	bool d;
 	unsigned long flags;
-	unsigned long flags1;
 	struct rcu_node *rnp = rdp->mynode;
 	struct rcu_node *rnp_root = rcu_get_root(rdp->rsp);
 
@@ -2236,8 +2235,8 @@
 						      c, rnp->level,
 						      rnp->grplo, rnp->grphi,
 						      "Startedroot");
-			local_save_flags(flags1);
-			rcu_start_gp(rdp->rsp, flags1); /* Rlses ->lock. */
+			rcu_start_gp(rdp->rsp);
+			raw_spin_unlock(&rnp->lock);
 		}
 
 		/* Clean up locking and irq state. */