livepatch: Replace synchronize_sched() with synchronize_rcu()

Now that synchronize_rcu() waits for preempt-disable regions of code
as well as RCU read-side critical sections, synchronize_sched() can be
replaced by synchronize_rcu().  This commit therefore makes this change,
even though it is but a comment.
Signed-off-by: NPaul E. McKenney <paulmck@linux.ibm.com>

kernel/livepatch/patch.c

@@ -61,7 +61,7 @@ static void notrace klp_ftrace_handler(unsigned long ip,
 	ops = container_of(fops, struct klp_ops, fops);
 
 	/*
-	 * A variant of synchronize_sched() is used to allow patching functions
+	 * A variant of synchronize_rcu() is used to allow patching functions
 	 * where RCU is not watching, see klp_synchronize_transition().
 	 */
 	preempt_disable_notrace();
@@ -72,7 +72,7 @@ static void notrace klp_ftrace_handler(unsigned long ip,
 	/*
 	 * func should never be NULL because preemption should be disabled here
 	 * and unregister_ftrace_function() does the equivalent of a
-	 * synchronize_sched() before the func_stack removal.
+	 * synchronize_rcu() before the func_stack removal.
 	 */
 	if (WARN_ON_ONCE(!func))
 		goto unlock;

kernel/livepatch/transition.c

@@ -52,7 +52,7 @@ static DECLARE_DELAYED_WORK(klp_transition_work, klp_transition_work_fn);
 
 /*
  * This function is just a stub to implement a hard force
- * of synchronize_sched(). This requires synchronizing
+ * of synchronize_rcu(). This requires synchronizing
  * tasks even in userspace and idle.
  */
 static void klp_sync(struct work_struct *work)
@@ -175,7 +175,7 @@ void klp_cancel_transition(void)
 void klp_update_patch_state(struct task_struct *task)
 {
 	/*
-	 * A variant of synchronize_sched() is used to allow patching functions
+	 * A variant of synchronize_rcu() is used to allow patching functions
 	 * where RCU is not watching, see klp_synchronize_transition().
 	 */
 	preempt_disable_notrace();