Merge branch 'for-3.11-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup

Pull cgroup changes from Tejun Heo:
 "This contains two patches, both of which aren't fixes per-se but I
  think it'd be better to fast-track them.

  One removes bcache_subsys_id which was added without proper review
  through the block tree.  Fortunately, bcache cgroup code is
  unconditionally disabled, so this was never exposed to userland.  The
  cgroup subsys_id is removed.  Kent will remove the affected (disabled)
  code through bcache branch.

  The other simplifies task_group_path_from_hierarchy().  The function
  doesn't currently have in-kernel users but there are external code and
  development going on dependent on the function and making the function
  available for 3.11 would make things go smoother"

* 'for-3.11-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup:
  cgroup: replace task_cgroup_path_from_hierarchy() with task_cgroup_path()
  cgroup: remove bcache_subsys_id which got added stealthily

include/linux/cgroup.h

@@ -542,8 +542,7 @@ 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);
 

include/linux/cgroup_subsys.h

-/* Add subsystem definitions of the form SUBSYS(<name>) in this
- * file. Surround each one by a line of comment markers so that
- * patches don't collide
+/*
+ * List of cgroup subsystems.
+ *
+ * DO NOT ADD ANY SUBSYSTEM WITHOUT EXPLICIT ACKS FROM CGROUP MAINTAINERS.
  */
-
-/* */
-
-/* */
-
 #if IS_SUBSYS_ENABLED(CONFIG_CPUSETS)
 SUBSYS(cpuset)
 #endif
 
-/* */
-
 #if IS_SUBSYS_ENABLED(CONFIG_CGROUP_DEBUG)
 SUBSYS(debug)
 #endif
 
-/* */
-
 #if IS_SUBSYS_ENABLED(CONFIG_CGROUP_SCHED)
 SUBSYS(cpu_cgroup)
 #endif
 
-/* */
-
 #if IS_SUBSYS_ENABLED(CONFIG_CGROUP_CPUACCT)
 SUBSYS(cpuacct)
 #endif
 
-/* */
-
 #if IS_SUBSYS_ENABLED(CONFIG_MEMCG)
 SUBSYS(mem_cgroup)
 #endif
 
-/* */
-
 #if IS_SUBSYS_ENABLED(CONFIG_CGROUP_DEVICE)
 SUBSYS(devices)
 #endif
 
-/* */
-
 #if IS_SUBSYS_ENABLED(CONFIG_CGROUP_FREEZER)
 SUBSYS(freezer)
 #endif
 
-/* */
-
 #if IS_SUBSYS_ENABLED(CONFIG_NET_CLS_CGROUP)
 SUBSYS(net_cls)
 #endif
 
-/* */
-
 #if IS_SUBSYS_ENABLED(CONFIG_BLK_CGROUP)
 SUBSYS(blkio)
 #endif
 
-/* */
-
 #if IS_SUBSYS_ENABLED(CONFIG_CGROUP_PERF)
 SUBSYS(perf)
 #endif
 
-/* */
-
 #if IS_SUBSYS_ENABLED(CONFIG_NETPRIO_CGROUP)
 SUBSYS(net_prio)
 #endif
 
-/* */
-
 #if IS_SUBSYS_ENABLED(CONFIG_CGROUP_HUGETLB)
 SUBSYS(hugetlb)
 #endif
-
-/* */
-
-#ifdef CONFIG_CGROUP_BCACHE
-SUBSYS(bcache)
-#endif
-
-/* */
+/*
+ * DO NOT ADD ANY SUBSYSTEM WITHOUT EXPLICIT ACKS FROM CGROUP MAINTAINERS.
+ */

kernel/cgroup.c

@@ -1845,36 +1845,43 @@ int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen)
 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