freezer_cg: disable writing freezer.state of root cgroup
With this change, control file 'freezer.state' doesn't exist in root
cgroup, making root cgroup unfreezable.
I think it's reasonable to disallow freeze tasks in the root cgroup. And
then we can avoid fork overhead when freezer subsystem is compiled but not
used.
Also make writing invalid value to freezer.state returns EINVAL rather
than EIO. This is more consistent with other cgroup subsystem.
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Acked-by: Paul Menage <menage@google.com>
Cc: Cedric Le Goater <clg@fr.ibm.com>
Cc: Paul Menage <menage@google.com>
Cc: Matt Helsley <matthltc@us.ibm.com>
Cc: "Serge E. Hallyn" <serue@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
index 6605907..fb249e2 100644
--- a/kernel/cgroup_freezer.c
+++ b/kernel/cgroup_freezer.c
@@ -192,6 +192,13 @@
*/
freezer = task_freezer(task);
+ /*
+ * The root cgroup is non-freezable, so we can skip the
+ * following check.
+ */
+ if (!freezer->css.cgroup->parent)
+ return;
+
spin_lock_irq(&freezer->lock);
BUG_ON(freezer->state == CGROUP_FROZEN);
@@ -335,7 +342,7 @@
else if (strcmp(buffer, freezer_state_strs[CGROUP_FROZEN]) == 0)
goal_state = CGROUP_FROZEN;
else
- return -EIO;
+ return -EINVAL;
if (!cgroup_lock_live_group(cgroup))
return -ENODEV;
@@ -354,6 +361,8 @@
static int freezer_populate(struct cgroup_subsys *ss, struct cgroup *cgroup)
{
+ if (!cgroup->parent)
+ return 0;
return cgroup_add_files(cgroup, ss, files, ARRAY_SIZE(files));
}