[PATCH, RFC, -rt] Make lockdep-RCU insist on rcu_read_lock_bh()

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

rcu: Make -rt complain about lack of rcu_read_lock_bh()

Mainline permits local_bh_disable() to be used in place of
rcu_read_lock_bh(), but this fails for CONFIG_PREEMPT_RT_FULL.  This
commit therefore makes rcu_read_lock_bh_held() insist on
rcu_read_lock_bh() for CONFIG_PREEMPT_RT_FULL.

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/rcupdate.c b/kernel/rcupdate.c
index 5e0577b..e91a85d 100644
--- a/kernel/rcupdate.c
+++ b/kernel/rcupdate.c
@@ -89,7 +89,11 @@ int rcu_read_lock_bh_held(void)
 {
 	if (!debug_lockdep_rcu_enabled())
 		return 1;
+#ifdef CONFIG_PREEMPT_RT_FULL
+	return lock_is_held(&rcu_bh_lock_map);
+#else
 	return in_softirq() || irqs_disabled();
+#endif
 }
 EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);
 #endif