2 files changed, 20 insertions, 14 deletions

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index fd097ecfcd97..21cfaff7e002 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -540,8 +540,7 @@ int cgroup_rm_cftypes(struct cgroup_subsys *ss, struct cftype *cfts);
 bool cgroup_is_descendant(struct cgroup *cgrp, struct cgroup *ancestor);
 
 int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen);
-int task_cgroup_path_from_hierarchy(struct task_struct *task, int hierarchy_id,
-                                    char *buf, size_t buflen);
+int task_cgroup_path(struct task_struct *task, char *buf, size_t buflen);
 
 int cgroup_task_count(const struct cgroup *cgrp);
 
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index e5583d10a325..afb8d53ca6c7 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1846,36 +1846,43 @@ out:
 EXPORT_SYMBOL_GPL(cgroup_path);
 
 /**
- * task_cgroup_path_from_hierarchy - cgroup path of a task on a hierarchy
+ * task_cgroup_path - cgroup path of a task in the first cgroup hierarchy
  * @task: target task
- * @hierarchy_id: the hierarchy to look up @task's cgroup from
  * @buf: the buffer to write the path into
  * @buflen: the length of the buffer
  *
- * Determine @task's cgroup on the hierarchy specified by @hierarchy_id and
- * copy its path into @buf.  This function grabs cgroup_mutex and shouldn't
- * be used inside locks used by cgroup controller callbacks.
+ * Determine @task's cgroup on the first (the one with the lowest non-zero
+ * hierarchy_id) cgroup hierarchy and copy its path into @buf.  This
+ * function grabs cgroup_mutex and shouldn't be used inside locks used by
+ * cgroup controller callbacks.
+ *
+ * Returns 0 on success, fails with -%ENAMETOOLONG if @buflen is too short.
  */
-int task_cgroup_path_from_hierarchy(struct task_struct *task, int hierarchy_id,
-                                    char *buf, size_t buflen)
+int task_cgroup_path(struct task_struct *task, char *buf, size_t buflen)
 {
         struct cgroupfs_root *root;
-        struct cgroup *cgrp = NULL;
-        int ret = -ENOENT;
+        struct cgroup *cgrp;
+        int hierarchy_id = 1, ret = 0;
+
+        if (buflen < 2)
+                return -ENAMETOOLONG;
 
         mutex_lock(&cgroup_mutex);
 
-        root = idr_find(&cgroup_hierarchy_idr, hierarchy_id);
+        root = idr_get_next(&cgroup_hierarchy_idr, &hierarchy_id);
+
         if (root) {
                 cgrp = task_cgroup_from_root(task, root);
                 ret = cgroup_path(cgrp, buf, buflen);
+        } else {
+                /* if no hierarchy exists, everyone is in "/" */
+                memcpy(buf, "/", 2);
         }
 
         mutex_unlock(&cgroup_mutex);
-
         return ret;
 }
-EXPORT_SYMBOL_GPL(task_cgroup_path_from_hierarchy);
+EXPORT_SYMBOL_GPL(task_cgroup_path);
 
 /*
  * Control Group taskset