[PATCH 1/3] cpuset: implement cgroup_rightmost_descendant()

Tejun Heo
2013-01-03T21:44:51Z

Implement cgroup_rightmost_descendant() which returns the right most
descendant of the specified cgroup. This can be used to skip the
cgroup's subtree while iterating with
cgroup_for_each_descendant_pre().

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Michal Hocko <mhocko@suse.cz>
---
include/linux/cgroup.h | 1 +
kernel/cgroup.c | 26 ++++++++++++++++++++++++++
2 files changed, 27 insertions(+)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 7d73905..860ca0f 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -558,6 +558,7 @@ static inline struct cgroup* task_cgroup(struct task_struct *task,

struct cgroup *cgroup_next_descendant_pre(struct cgroup *pos,
struct cgroup *cgroup);
+struct cgroup *cgroup_rightmost_descendant(struct cgroup *pos);

/**
* cgroup_for_each_descendant_pre - pre-order walk of a cgroup's descendants
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 4855892..6643f70 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -3017,6 +3017,32 @@ struct cgroup *cgroup_next_descendant_pre(struct cgroup *pos,
}
EXPORT_SYMBOL_GPL(cgroup_next_descendant_pre);

+/**
+ * cgroup_rightmost_descendant - return the rightmost descendant of a cgroup
+ * @pos: cgroup of interest
+ *
+ * Return the rightmost descendant of @pos. If there's no descendant,
+ * @pos is returned. This can be used during pre-order traversal to skip
+ * subtree of @pos.
+ */
+struct cgroup *cgroup_rightmost_descendant(struct cgroup *pos)
+{
+ struct cgroup *last, *tmp;
+
+ WARN_ON_ONCE(!rcu_read_lock_held());
+
+ do {
+ last = pos;
+ /* ->prev isn't RCU safe, walk ->next till the end */
+ pos = NULL;
+ list_for_each_entry_rcu(tmp, &last->children, sibling)
+ pos = tmp;
+ } while (pos);
+
+ return last;
+}
+EXPORT_SYMBOL_GPL(cgroup_rightmost_descendant);
+
static struct cgroup *cgroup_leftmost_descendant(struct cgroup *pos)
{
struct cgroup *last;
--
1.8.0.2