user namespaces: document CFS behavior

Documented the currently bogus state of support for CFS user groups with
user namespaces.  In particular, all users in a user namespace should be
children of the user which created the user namespace.  This is yet to
be implemented.

Signed-off-by: Serge E. Hallyn <serue@us.ibm.com>
Acked-by: Dhaval Giani <dhaval@linux.vnet.ibm.com>

Signed-off-by: Serge E. Hallyn <serue@us.ibm.com>
Signed-off-by: James Morris <jmorris@namei.org>

kernel/user.c

diff --git a/kernel/user.c b/kernel/user.c
index 6c924bc..6608a3d 100644
--- a/kernel/user.c
+++ b/kernel/user.c
@@ -239,7 +239,13 @@
 	.release = uids_release,
 };
 
-/* create /sys/kernel/uids/<uid>/cpu_share file for this user */
+/*
+ * Create /sys/kernel/uids/<uid>/cpu_share file for this user
+ * We do not create this file for users in a user namespace (until
+ * sysfs tagging is implemented).
+ *
+ * See Documentation/scheduler/sched-design-CFS.txt for ramifications.
+ */
 static int uids_user_create(struct user_struct *up)
 {
 	struct kobject *kobj = &up->kobj;