cgroup: enable refcnting for root csses
Currently, css_get(), css_tryget() and css_tryget_online() are noops
for root csses as an optimization; however, we're planning to use css
refcnts to track of cgroup lifetime too and root cgroups also need to
be reference counted. Since css has been converted to percpu_refcnt,
the overhead of refcnting is miniscule and this optimization isn't too
meaningful anymore. Furthermore, controllers which optimize the root
cgroup often never even invoke these functions in their hot paths.
This patch enables refcnting for root csses too. This makes CSS_ROOT
flag unused and removes it.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index e694f41..cb5864e 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -4158,8 +4158,6 @@
if (cgrp->parent) {
css->parent = cgroup_css(cgrp->parent, ss);
css_get(css->parent);
- } else {
- css->flags |= CSS_ROOT;
}
BUG_ON(cgroup_css(cgrp, ss));
@@ -4582,9 +4580,10 @@
BUG_ON(IS_ERR(css));
init_and_link_css(css, ss, &cgrp_dfl_root.cgrp);
if (early) {
- /* idr_alloc() can't be called safely during early init */
+ /* allocation can't be done safely during early init */
css->id = 1;
} else {
+ BUG_ON(percpu_ref_init(&css->refcnt, css_release));
css->id = cgroup_idr_alloc(&ss->css_idr, css, 1, 2, GFP_KERNEL);
BUG_ON(css->id < 0);
}
@@ -4671,6 +4670,7 @@
struct cgroup_subsys_state *css =
init_css_set.subsys[ss->id];
+ BUG_ON(percpu_ref_init(&css->refcnt, css_release));
css->id = cgroup_idr_alloc(&ss->css_idr, css, 1, 2,
GFP_KERNEL);
BUG_ON(css->id < 0);