rcu: Update docs to include kfree_rcu()

Mention kfree_rcu() in the call_rcu() section. Additionally fix the
example code for list replacement that used the wrong structure element.

Signed-off-by: Kees Cook <[e-mail]>
Signed-off-by: Paul E. McKenney <[e-mail]>

Documentation/RCU/listRCU.txt

···
 				audit_copy_rule(&ne->rule, &e->rule);
 				ne->rule.action = newaction;
 				ne->rule.file_count = newfield_count;
-				list_replace_rcu(e, ne);
+				list_replace_rcu(&e->list, &ne->list);
 				call_rcu(&e->rcu, audit_free_rule);
 				return 0;
 			}

Documentation/RCU/whatisRCU.txt

···
 	{
 		struct foo *fp = container_of(rp, struct foo, rcu);
 
+		foo_cleanup(fp->a);
+
 		kfree(fp);
 	}
 
···
 	function that will be invoked after the completion of all RCU
 	read-side critical sections that might be referencing that
 	data item.
+
+If the callback for call_rcu() is not doing anything more than calling
+kfree() on the structure, you can use kfree_rcu() instead of call_rcu()
+to avoid having to write your own callback:
+
+	kfree_rcu(old_fp, rcu);
 
 Again, see checklist.txt for additional rules governing the use of RCU.
 
···
 
 Also, the presence of synchronize_rcu() means that the RCU version of
 delete() can now block.  If this is a problem, there is a callback-based
-mechanism that never blocks, namely call_rcu(), that can be used in
-place of synchronize_rcu().
+mechanism that never blocks, namely call_rcu() or kfree_rcu(), that can
+be used in place of synchronize_rcu().
 
 
 7.  FULL LIST OF RCU APIs
···
 	rcu_read_unlock		synchronize_rcu
 	rcu_dereference		synchronize_rcu_expedited
 				call_rcu
+				kfree_rcu
 
 
 bh:	Critical sections	Grace period		Barrier