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@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxx>
---
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 c02b055..bbf7460 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -3009,6 +3009,32 @@ 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
+ * @cgrp: cgroup of interest
+ *
+ * Return the rightmost descendant of @cgrp. If there's no descendant,
+ * @cgrp is returned. This can be used during pre-order traversal to skip
+ * subtree of @cgrp.
+ */
+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;
--
1.7.11.7
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