cgroup: make css_next_child() skip missing csses
css_next_child() walks the children of the specified css. It does
this by finding the next cgroup and then returning the requested css.
On the default unified hierarchy, a cgroup may not have a css
associated with it even if the hierarchy has the subsystem enabled.
This patch updates css_next_child() so that it skips children without
the requested css associated.
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 37d9662..0edc186 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2708,10 +2708,19 @@
break;
}
- if (&next->sibling == &cgrp->children)
- return NULL;
+ /*
+ * @next, if not pointing to the head, can be dereferenced and is
+ * the next sibling; however, it might have @ss disabled. If so,
+ * fast-forward to the next enabled one.
+ */
+ while (&next->sibling != &cgrp->children) {
+ struct cgroup_subsys_state *next_css = cgroup_css(next, parent_css->ss);
- return cgroup_css(next, parent_css->ss);
+ if (next_css)
+ return next_css;
+ next = list_entry_rcu(next->sibling.next, struct cgroup, sibling);
+ }
+ return NULL;
}
/**
