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Subject[PATCH 04/12] cgroup: make css_next_child() skip missing csses
Date
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>
---
kernel/cgroup.c | 15 ++++++++++++---
1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 29e8698..f525578 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2712,10 +2712,19 @@ css_next_child(struct cgroup_subsys_state *pos_css,
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;
}

/**
--
1.9.0


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