diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 9ce682242e99..3bee58fc23b1 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3280,12 +3280,6 @@ static inline int rcu_blocking_is_gp(void)
  * to have executed a full memory barrier during the execution of
  * synchronize_sched() -- even if CPU A and CPU B are the same CPU (but
  * again only if the system has more than one CPU).
- *
- * This primitive provides the guarantees made by the (now removed)
- * synchronize_kernel() API.  In contrast, synchronize_rcu() only
- * guarantees that rcu_read_lock() sections will have completed.
- * In "classic RCU", these two guarantees happen to be one and
- * the same, but can differ in realtime RCU implementations.
  */
 void synchronize_sched(void)
 {
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index a421753e8e9c..3b432fa4c45b 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -664,8 +664,13 @@ EXPORT_SYMBOL_GPL(call_rcu);
  * synchronize_rcu() was waiting.  RCU read-side critical sections are
  * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested.
  *
- * See the description of synchronize_sched() for more detailed information
- * on memory ordering guarantees.
+ * See the description of synchronize_sched() for more detailed
+ * information on memory-ordering guarantees.  However, please note
+ * that -only- the memory-ordering guarantees apply.  For example,
+ * synchronize_rcu() is -not- guaranteed to wait on things like code
+ * protected by preempt_disable(), instead, synchronize_rcu() is -only-
+ * guaranteed to wait on RCU read-side critical sections, that is, sections
+ * of code protected by rcu_read_lock().
  */
 void synchronize_rcu(void)
 {