move d_rcu from overlapping d_child to overlapping d_alias

commit 946e51f2bf37f1656916eb75bd0742ba33983c28 upstream.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
[bwh: Backported to 3.2:
 - Apply name changes in all the different places we use d_alias and d_child
 - Move the WARN_ON() in __d_free() to d_free() as we don't have dentry_free()]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
[lizf: Backported to 3.4:
 - adjust context
 - need one more name change in debugfs]
diff --git a/fs/autofs4/root.c b/fs/autofs4/root.c
index 8c4292f..4117604 100644
--- a/fs/autofs4/root.c
+++ b/fs/autofs4/root.c
@@ -651,7 +651,7 @@
 	/* only consider parents below dentrys in the root */
 	if (IS_ROOT(parent->d_parent))
 		return;
-	d_child = &dentry->d_u.d_child;
+	d_child = &dentry->d_child;
 	/* Set parent managed if it's becoming empty */
 	if (d_child->next == &parent->d_subdirs &&
 	    d_child->prev == &parent->d_subdirs)