[PATCHv3 3/8] cgroup: add function to get task's cgroup on default hierarchy

[Aditya Kali]

get_task_cgroup() returns the (reference counted) cgroup of the
given task on the default hierarchy.

Acked-by: Serge Hallyn <serge.hallyn@xxxxxxxxxxxxx>
Signed-off-by: Aditya Kali <adityakali@xxxxxxxxxx>
---
 include/linux/cgroup.h |  1 +
 kernel/cgroup.c        | 25 +++++++++++++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 9fd99f5..d6930de 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -579,6 +579,7 @@ static inline void pr_cont_cgroup_path(struct cgroup *cgrp)
 }
 
 char *task_cgroup_path(struct task_struct *task, char *buf, size_t buflen);
+struct cgroup *get_task_cgroup(struct task_struct *task);
 
 int cgroup_add_dfl_cftypes(struct cgroup_subsys *ss, struct cftype *cfts);
 int cgroup_add_legacy_cftypes(struct cgroup_subsys *ss, struct cftype *cfts);
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index bb263d0..5d8fc84 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1966,6 +1966,31 @@ char *task_cgroup_path(struct task_struct *task, char *buf, size_t buflen)
 }
 EXPORT_SYMBOL_GPL(task_cgroup_path);
 
+/*
+ * get_task_cgroup - returns the cgroup of the task in the default cgroup
+ * hierarchy.
+ *
+ * @task: target task
+ * This function returns the @task's cgroup on the default cgroup hierarchy. The
+ * returned cgroup has its reference incremented (by calling cgroup_get()). So
+ * the caller must cgroup_put() the obtained reference once it is done with it.
+ */
+struct cgroup *get_task_cgroup(struct task_struct *task)
+{
+	struct cgroup *cgrp;
+
+	mutex_lock(&cgroup_mutex);
+	down_read(&css_set_rwsem);
+
+	cgrp = task_cgroup_from_root(task, &cgrp_dfl_root);
+	cgroup_get(cgrp);
+
+	up_read(&css_set_rwsem);
+	mutex_unlock(&cgroup_mutex);
+	return cgrp;
+}
+EXPORT_SYMBOL_GPL(get_task_cgroup);
+
 /* used to track tasks and other necessary states during migration */
 struct cgroup_taskset {
 	/* the src and dst cset list running through cset->mg_node */
-- 
2.2.0.rc0.207.ga3a616c

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