cgroup: add css_set->dfl_cgrp

To implement the unified hierarchy behavior, we'll need to be able to
determine the associated cgroup on the default hierarchy from css_set.
Let's add css_set->dfl_cgrp so that it can be accessed conveniently
and efficiently.

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

1 files changed, 4 insertions, 0 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 2a4f88db3205..c66bfc8ee8a7 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -651,6 +651,10 @@ static void link_css_set(struct list_head *tmp_links, struct css_set *cset,
         struct cgrp_cset_link *link;
 
         BUG_ON(list_empty(tmp_links));
+
+        if (cgroup_on_dfl(cgrp))
+                cset->dfl_cgrp = cgrp;
+
         link = list_first_entry(tmp_links, struct cgrp_cset_link, cset_link);
         link->cset = cset;
         link->cgrp = cgrp;