From ce5750075a62130d3a154e0105332607ceb49f56 Mon Sep 17 00:00:00 2001
From: Li Zefan <lizefan@huawei.com>
Date: Tue, 5 Mar 2013 10:57:03 +0800
Subject: [PATCH] --- yaml --- r: 365563 b: refs/heads/master c:
 7d8e0bf56a66bab08d2f316dd87e56c08cecb899 h: refs/heads/master i:   365561:
 91eb0877c5445d65633318ebe35a6ca5480241b7   365559:
 b79c7acea50904ae0021408fdaca771ce99b0bf5 v: v3

---
 [refs]                       |  2 +-
 trunk/include/linux/cgroup.h | 17 ++++++++++++++---
 trunk/kernel/cgroup.c        | 28 ++++++++++++++--------------
 3 files changed, 29 insertions(+), 18 deletions(-)

diff --git a/[refs] b/[refs]
index 77cbc663c6f1..beeb161f5d6f 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: f50daa704f36a6544a902c52b6cf37b0493dfc5d
+refs/heads/master: 7d8e0bf56a66bab08d2f316dd87e56c08cecb899
diff --git a/trunk/include/linux/cgroup.h b/trunk/include/linux/cgroup.h
index 75c6ec1ba1ba..5f76829dd75e 100644
--- a/trunk/include/linux/cgroup.h
+++ b/trunk/include/linux/cgroup.h
@@ -44,14 +44,25 @@ extern void cgroup_unload_subsys(struct cgroup_subsys *ss);
 
 extern const struct file_operations proc_cgroup_operations;
 
-/* Define the enumeration of all builtin cgroup subsystems */
+/*
+ * Define the enumeration of all cgroup subsystems.
+ *
+ * We define ids for builtin subsystems and then modular ones.
+ */
 #define SUBSYS(_x) _x ## _subsys_id,
-#define IS_SUBSYS_ENABLED(option) IS_ENABLED(option)
 enum cgroup_subsys_id {
+#define IS_SUBSYS_ENABLED(option) IS_BUILTIN(option)
+#include <linux/cgroup_subsys.h>
+#undef IS_SUBSYS_ENABLED
+	CGROUP_BUILTIN_SUBSYS_COUNT,
+
+	__CGROUP_SUBSYS_TEMP_PLACEHOLDER = CGROUP_BUILTIN_SUBSYS_COUNT - 1,
+
+#define IS_SUBSYS_ENABLED(option) IS_MODULE(option)
 #include <linux/cgroup_subsys.h>
+#undef IS_SUBSYS_ENABLED
 	CGROUP_SUBSYS_COUNT,
 };
-#undef IS_SUBSYS_ENABLED
 #undef SUBSYS
 
 /* Per-subsystem/per-cgroup state maintained by the system. */
diff --git a/trunk/kernel/cgroup.c b/trunk/kernel/cgroup.c
index 9df799d5d31c..7a6c4c72ca55 100644
--- a/trunk/kernel/cgroup.c
+++ b/trunk/kernel/cgroup.c
@@ -4940,17 +4940,17 @@ void cgroup_post_fork(struct task_struct *child)
 	 * and addition to css_set.
 	 */
 	if (need_forkexit_callback) {
-		for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
+		/*
+		 * fork/exit callbacks are supported only for builtin
+		 * subsystems, and the builtin section of the subsys
+		 * array is immutable, so we don't need to lock the
+		 * subsys array here. On the other hand, modular section
+		 * of the array can be freed at module unload, so we
+		 * can't touch that.
+		 */
+		for (i = 0; i < CGROUP_BUILTIN_SUBSYS_COUNT; i++) {
 			struct cgroup_subsys *ss = subsys[i];
 
-			/*
-			 * fork/exit callbacks are supported only for
-			 * builtin subsystems and we don't need further
-			 * synchronization as they never go away.
-			 */
-			if (!ss || ss->module)
-				continue;
-
 			if (ss->fork)
 				ss->fork(child);
 		}
@@ -5015,13 +5015,13 @@ void cgroup_exit(struct task_struct *tsk, int run_callbacks)
 	tsk->cgroups = &init_css_set;
 
 	if (run_callbacks && need_forkexit_callback) {
-		for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
+		/*
+		 * fork/exit callbacks are supported only for builtin
+		 * subsystems, see cgroup_post_fork() for details.
+		 */
+		for (i = 0; i < CGROUP_BUILTIN_SUBSYS_COUNT; i++) {
 			struct cgroup_subsys *ss = subsys[i];
 
-			/* modular subsystems can't use callbacks */
-			if (!ss || ss->module)
-				continue;
-
 			if (ss->exit) {
 				struct cgroup *old_cgrp =
 					rcu_dereference_raw(cg->subsys[i])->cgroup;