cgroup: move ->subsys_mask from cgroupfs_root to cgroup

cgroupfs_root->subsys_mask represents the controllers attached to the
hierarchy.  This patch moves the field to cgroup.  Subsystem
initialization and rebinding updates the top cgroup's subsys_mask.
For !root cgroups, the subsys_mask bits are set from create_css() and
cleared from kill_css(), which effectively means that all cgroups will
have the same subsys_mask as the top cgroup.

While this doesn't make any difference now, this will help
implementation of the default unified hierarchy where !root cgroups
may have subsets of the top_cgroup's subsys_mask.

While at it, __kill_css() is split out of kill_css().  The former
doesn't care about the subsys_mask while the latter becomes noop if
the controller is already killed and clears the matching bit if not
before proceeding to killing the css.  This will be used later by the
default unified hierarchy implementation.

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

1 files changed, 3 insertions, 3 deletions

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 9f4f253f0e47..3752a0182c94 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -173,6 +173,9 @@ struct cgroup {
 	 */
 	u64 serial_nr;
 
+	/* The bitmask of subsystems attached to this cgroup */
+	unsigned long subsys_mask;
+
 	/* Private pointers for each registered subsystem */
 	struct cgroup_subsys_state __rcu *subsys[CGROUP_SUBSYS_COUNT];
 
@@ -276,9 +279,6 @@ enum {
 struct cgroupfs_root {
 	struct kernfs_root *kf_root;
 
-	/* The bitmask of subsystems attached to this hierarchy */
-	unsigned long subsys_mask;
-
 	/* Unique id for this hierarchy. */
 	int hierarchy_id;