8 files changed, 55 insertions, 20 deletions
diff --git a/block/Kconfig b/block/Kconfig
index e20fbde0875..62a5921321c 100644
--- a/block/Kconfig
+++ b/block/Kconfig
@@ -78,7 +78,7 @@ config BLK_DEV_INTEGRITY
 	Protection.  If in doubt, say N.
 
 config BLK_CGROUP
-	bool
+	tristate
 	depends on CGROUPS
 	default n
 	---help---
diff --git a/block/Kconfig.iosched b/block/Kconfig.iosched
index b71abfb0d72..fc71cf071fb 100644
--- a/block/Kconfig.iosched
+++ b/block/Kconfig.iosched
@@ -23,6 +23,7 @@ config IOSCHED_DEADLINE
 
 config IOSCHED_CFQ
 	tristate "CFQ I/O scheduler"
+	select BLK_CGROUP if CFQ_GROUP_IOSCHED
 	default y
 	---help---
 	  The CFQ I/O scheduler tries to distribute bandwidth equally
@@ -35,7 +36,6 @@ config IOSCHED_CFQ
 config CFQ_GROUP_IOSCHED
 	bool "CFQ Group Scheduling support"
 	depends on IOSCHED_CFQ && CGROUPS
-	select BLK_CGROUP
 	default n
 	---help---
 	  Enable group IO scheduling in CFQ.
diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index c85d74cae20..4b686ad08ea 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -23,6 +23,31 @@ static LIST_HEAD(blkio_list);
 struct blkio_cgroup blkio_root_cgroup = { .weight = 2*BLKIO_WEIGHT_DEFAULT };
 EXPORT_SYMBOL_GPL(blkio_root_cgroup);
 
+static struct cgroup_subsys_state *blkiocg_create(struct cgroup_subsys *,
+						  struct cgroup *);
+static int blkiocg_can_attach(struct cgroup_subsys *, struct cgroup *,
+			      struct task_struct *, bool);
+static void blkiocg_attach(struct cgroup_subsys *, struct cgroup *,
+			   struct cgroup *, struct task_struct *, bool);
+static void blkiocg_destroy(struct cgroup_subsys *, struct cgroup *);
+static int blkiocg_populate(struct cgroup_subsys *, struct cgroup *);
+
+struct cgroup_subsys blkio_subsys = {
+	.name = "blkio",
+	.create = blkiocg_create,
+	.can_attach = blkiocg_can_attach,
+	.attach = blkiocg_attach,
+	.destroy = blkiocg_destroy,
+	.populate = blkiocg_populate,
+#ifdef CONFIG_BLK_CGROUP
+	/* note: blkio_subsys_id is otherwise defined in blk-cgroup.h */
+	.subsys_id = blkio_subsys_id,
+#endif
+	.use_id = 1,
+	.module = THIS_MODULE,
+};
+EXPORT_SYMBOL_GPL(blkio_subsys);
+
 struct blkio_cgroup *cgroup_to_blkio_cgroup(struct cgroup *cgroup)
 {
 	return container_of(cgroup_subsys_state(cgroup, blkio_subsys_id),
@@ -253,7 +278,8 @@ remove_entry:
 done:
 	free_css_id(&blkio_subsys, &blkcg->css);
 	rcu_read_unlock();
-	kfree(blkcg);
+	if (blkcg != &blkio_root_cgroup)
+		kfree(blkcg);
 }
 
 static struct cgroup_subsys_state *
@@ -319,17 +345,6 @@ static void blkiocg_attach(struct cgroup_subsys *subsys, struct cgroup *cgroup,
 	task_unlock(tsk);
 }
 
-struct cgroup_subsys blkio_subsys = {
-	.name = "blkio",
-	.create = blkiocg_create,
-	.can_attach = blkiocg_can_attach,
-	.attach = blkiocg_attach,
-	.destroy = blkiocg_destroy,
-	.populate = blkiocg_populate,
-	.subsys_id = blkio_subsys_id,
-	.use_id = 1,
-};
-
 void blkio_policy_register(struct blkio_policy_type *blkiop)
 {
 	spin_lock(&blkio_list_lock);
@@ -345,3 +360,17 @@ void blkio_policy_unregister(struct blkio_policy_type *blkiop)
 	spin_unlock(&blkio_list_lock);
 }
 EXPORT_SYMBOL_GPL(blkio_policy_unregister);
+
+static int __init init_cgroup_blkio(void)
+{
+	return cgroup_load_subsys(&blkio_subsys);
+}
+
+static void __exit exit_cgroup_blkio(void)
+{
+	cgroup_unload_subsys(&blkio_subsys);
+}
+
+module_init(init_cgroup_blkio);
+module_exit(exit_cgroup_blkio);
+MODULE_LICENSE("GPL");
diff --git a/block/blk-cgroup.h b/block/blk-cgroup.h
index 84bf745fa77..8ccc20464da 100644
--- a/block/blk-cgroup.h
+++ b/block/blk-cgroup.h
@@ -15,7 +15,13 @@
 
 #include <linux/cgroup.h>
 
-#ifdef CONFIG_BLK_CGROUP
+#if defined(CONFIG_BLK_CGROUP) || defined(CONFIG_BLK_CGROUP_MODULE)
+
+#ifndef CONFIG_BLK_CGROUP
+/* When blk-cgroup is a module, its subsys_id isn't a compile-time constant */
+extern struct cgroup_subsys blkio_subsys;
+#define blkio_subsys_id blkio_subsys.subsys_id
+#endif
 
 struct blkio_cgroup {
 	struct cgroup_subsys_state css;
@@ -91,7 +97,7 @@ static inline void blkiocg_update_blkio_group_dequeue_stats(
 			struct blkio_group *blkg, unsigned long dequeue) {}
 #endif
 
-#ifdef CONFIG_BLK_CGROUP
+#if defined(CONFIG_BLK_CGROUP) || defined(CONFIG_BLK_CGROUP_MODULE)
 extern struct blkio_cgroup blkio_root_cgroup;
 extern struct blkio_cgroup *cgroup_to_blkio_cgroup(struct cgroup *cgroup);
 extern void blkiocg_add_blkio_group(struct blkio_cgroup *blkcg,
diff --git a/block/blk-integrity.c b/block/blk-integrity.c
index 15c630813b1..96e83c2bdb9 100644
--- a/block/blk-integrity.c
+++ b/block/blk-integrity.c
@@ -278,7 +278,7 @@ static struct attribute *integrity_attrs[] = {
 	NULL,
 };
 
-static struct sysfs_ops integrity_ops = {
+static const struct sysfs_ops integrity_ops = {
 	.show	= &integrity_attr_show,
 	.store	= &integrity_attr_store,
 };
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index e85442415db..2ae2cb3f362 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -450,7 +450,7 @@ static void blk_release_queue(struct kobject *kobj)
 	kmem_cache_free(blk_requestq_cachep, q);
 }
 
-static struct sysfs_ops queue_sysfs_ops = {
+static const struct sysfs_ops queue_sysfs_ops = {
 	.show	= queue_attr_show,
 	.store	= queue_attr_store,
 };
diff --git a/block/bsg.c b/block/bsg.c
index a9fd2d84b53..46597a6bd11 100644
--- a/block/bsg.c
+++ b/block/bsg.c
@@ -260,7 +260,7 @@ bsg_map_hdr(struct bsg_device *bd, struct sg_io_v4 *hdr, fmode_t has_write_perm,
 		return ERR_PTR(ret);
 
 	/*
-	 * map scatter-gather elements seperately and string them to request
+	 * map scatter-gather elements separately and string them to request
 	 */
 	rq = blk_get_request(q, rw, GFP_KERNEL);
 	if (!rq)
diff --git a/block/elevator.c b/block/elevator.c
index ee3a883840f..df75676f667 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -892,7 +892,7 @@ elv_attr_store(struct kobject *kobj, struct attribute *attr,
 	return error;
 }
 
-static struct sysfs_ops elv_sysfs_ops = {
+static const struct sysfs_ops elv_sysfs_ops = {
 	.show	= elv_attr_show,
 	.store	= elv_attr_store,
 };