cgroup: introduce cgroup_{save|propagate|restore}_control()

While controllers are being enabled and disabled in
cgroup_subtree_control_write(), the original subsystem masks are
stashed in local variables so that they can be restored if the
operation fails in the middle.

This patch adds dedicated fields to struct cgroup to be used instead
of the local variables and implements functions to stash the current
values, propagate the changes and restore them recursively.  Combined
with the previous changes, this makes subsystem management operations
fully recursive and modularlized.  This will be used to expand cgroup
core functionalities.

While at it, remove now unused @css_enable and @css_disable from
cgroup_subtree_control_write().

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Zefan Li <lizefan@huawei.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
index 7593c1a46786..aae8c94de4b3 100644
--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -260,6 +260,8 @@ struct cgroup {
 	 */
 	u16 subtree_control;
 	u16 subtree_ss_mask;
+	u16 old_subtree_control;
+	u16 old_subtree_ss_mask;
 
 	/* Private pointers for each registered subsystem */
 	struct cgroup_subsys_state __rcu *subsys[CGROUP_SUBSYS_COUNT];