rcu: Tighten rcu_lockdep_assert_cblist_protected() check

The ->nocb_lock lockdep assertion is currently guarded by cpu_online(),
which is incorrect for no-CBs CPUs, whose callback lists must be
protected by ->nocb_lock regardless of whether or not the corresponding
CPU is online.  This situation could result in failure to detect bugs
resulting from failing to hold ->nocb_lock for offline CPUs.

This commit therefore removes the cpu_online() guard.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

kernel/rcu/tree_plugin.h

@@ -1579,8 +1579,7 @@ static void rcu_nocb_unlock_irqrestore(struct rcu_data *rdp,
 static void rcu_lockdep_assert_cblist_protected(struct rcu_data *rdp)
 {
 	lockdep_assert_irqs_disabled();
-	if (rcu_segcblist_is_offloaded(&rdp->cblist) &&
-	    cpu_online(rdp->cpu))
+	if (rcu_segcblist_is_offloaded(&rdp->cblist))
 		lockdep_assert_held(&rdp->nocb_lock);
 }