cgroup: clean up cgroup_subsys names and initialization

cgroup_subsys is a bit messier than it needs to be.

* The name of a subsys can be different from its internal identifier
  defined in cgroup_subsys.h.  Most subsystems use the matching name
  but three - cpu, memory and perf_event - use different ones.

* cgroup_subsys_id enums are postfixed with _subsys_id and each
  cgroup_subsys is postfixed with _subsys.  cgroup.h is widely
  included throughout various subsystems, it doesn't and shouldn't
  have claim on such generic names which don't have any qualifier
  indicating that they belong to cgroup.

* cgroup_subsys->subsys_id should always equal the matching
  cgroup_subsys_id enum; however, we require each controller to
  initialize it and then BUG if they don't match, which is a bit
  silly.

This patch cleans up cgroup_subsys names and initialization by doing
the followings.

* cgroup_subsys_id enums are now postfixed with _cgrp_id, and each
  cgroup_subsys with _cgrp_subsys.

* With the above, renaming subsys identifiers to match the userland
  visible names doesn't cause any naming conflicts.  All non-matching
  identifiers are renamed to match the official names.

  cpu_cgroup -> cpu
  mem_cgroup -> memory
  perf -> perf_event

* controllers no longer need to initialize ->subsys_id and ->name.
  They're generated in cgroup core and set automatically during boot.

* Redundant cgroup_subsys declarations removed.

* While updating BUG_ON()s in cgroup_init_early(), convert them to
  WARN()s.  BUGging that early during boot is stupid - the kernel
  can't print anything, even through serial console and the trap
  handler doesn't even link stack frame properly for back-tracing.

This patch doesn't introduce any behavior changes.

v2: Rebased on top of fe1217c4f3f7 ("net: net_cls: move cgroupfs
    classid handling into core").

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Acked-by: "David S. Miller" <davem@davemloft.net>
Acked-by: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Acked-by: Michal Hocko <mhocko@suse.cz>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Aristeu Rozanski <aris@redhat.com>
Acked-by: Ingo Molnar <mingo@redhat.com>
Acked-by: Li Zefan <lizefan@huawei.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Serge E. Hallyn <serue@us.ibm.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Thomas Graf <tgraf@suug.ch>

6 files changed, 33 insertions, 39 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index ccb16b4..fe3f725 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -120,10 +120,18 @@ static struct workqueue_struct *cgroup_destroy_wq;
 static struct workqueue_struct *cgroup_pidlist_destroy_wq;
 
 /* generate an array of cgroup subsystem pointers */
-#define SUBSYS(_x) [_x ## _subsys_id] = &_x ## _subsys,
+#define SUBSYS(_x) [_x ## _cgrp_id] = &_x ## _cgrp_subsys,
 static struct cgroup_subsys *cgroup_subsys[] = {
 #include <linux/cgroup_subsys.h>
 };
+#undef SUBSYS
+
+/* array of cgroup subsystem names */
+#define SUBSYS(_x) [_x ## _cgrp_id] = #_x,
+static const char *cgroup_subsys_name[] = {
+#include <linux/cgroup_subsys.h>
+};
+#undef SUBSYS
 
 /*
  * The dummy hierarchy, reserved for the subsystems that are otherwise
@@ -1076,7 +1084,7 @@ static int parse_cgroupfs_options(char *data, struct cgroup_sb_opts *opts)
 	BUG_ON(!mutex_is_locked(&cgroup_mutex));
 
 #ifdef CONFIG_CPUSETS
-	mask = ~(1UL << cpuset_subsys_id);
+	mask = ~(1UL << cpuset_cgrp_id);
 #endif
 
 	memset(opts, 0, sizeof(*opts));
@@ -4528,15 +4536,15 @@ int __init cgroup_init_early(void)
 	list_add(&init_cgrp_cset_link.cgrp_link, &init_css_set.cgrp_links);
 
 	for_each_subsys(ss, i) {
-		BUG_ON(!ss->name);
-		BUG_ON(strlen(ss->name) > MAX_CGROUP_TYPE_NAMELEN);
-		BUG_ON(!ss->css_alloc);
-		BUG_ON(!ss->css_free);
-		if (ss->subsys_id != i) {
-			printk(KERN_ERR "cgroup: Subsys %s id == %d\n",
-			       ss->name, ss->subsys_id);
-			BUG();
-		}
+		WARN(!ss->css_alloc || !ss->css_free || ss->name || ss->subsys_id,
+		     "invalid cgroup_subsys %d:%s css_alloc=%p css_free=%p name:id=%d:%s\n",
+		     i, cgroup_subsys_name[i], ss->css_alloc, ss->css_free,
+		     ss->subsys_id, ss->name);
+		WARN(strlen(cgroup_subsys_name[i]) > MAX_CGROUP_TYPE_NAMELEN,
+		     "cgroup_subsys_name %s too long\n", cgroup_subsys_name[i]);
+
+		ss->subsys_id = i;
+		ss->name = cgroup_subsys_name[i];
 
 		if (ss->early_init)
 			cgroup_init_subsys(ss);
@@ -5167,11 +5175,9 @@ static struct cftype debug_files[] =  {
 	{ }	/* terminate */
 };
 
-struct cgroup_subsys debug_subsys = {
-	.name = "debug",
+struct cgroup_subsys debug_cgrp_subsys = {
 	.css_alloc = debug_css_alloc,
 	.css_free = debug_css_free,
-	.subsys_id = debug_subsys_id,
 	.base_cftypes = debug_files,
 };
 #endif /* CONFIG_CGROUP_DEBUG */
diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
index 6c3154e..98ea26a9 100644
--- a/kernel/cgroup_freezer.c
+++ b/kernel/cgroup_freezer.c
@@ -52,7 +52,7 @@ static inline struct freezer *css_freezer(struct cgroup_subsys_state *css)
 
 static inline struct freezer *task_freezer(struct task_struct *task)
 {
-	return css_freezer(task_css(task, freezer_subsys_id));
+	return css_freezer(task_css(task, freezer_cgrp_id));
 }
 
 static struct freezer *parent_freezer(struct freezer *freezer)
@@ -84,8 +84,6 @@ static const char *freezer_state_strs(unsigned int state)
 	return "THAWED";
 };
 
-struct cgroup_subsys freezer_subsys;
-
 static struct cgroup_subsys_state *
 freezer_css_alloc(struct cgroup_subsys_state *parent_css)
 {
@@ -473,13 +471,11 @@ static struct cftype files[] = {
 	{ }	/* terminate */
 };
 
-struct cgroup_subsys freezer_subsys = {
-	.name		= "freezer",
+struct cgroup_subsys freezer_cgrp_subsys = {
 	.css_alloc	= freezer_css_alloc,
 	.css_online	= freezer_css_online,
 	.css_offline	= freezer_css_offline,
 	.css_free	= freezer_css_free,
-	.subsys_id	= freezer_subsys_id,
 	.attach		= freezer_attach,
 	.fork		= freezer_fork,
 	.base_cftypes	= files,
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 4410ac6..2d018c7 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -119,7 +119,7 @@ static inline struct cpuset *css_cs(struct cgroup_subsys_state *css)
 /* Retrieve the cpuset for a task */
 static inline struct cpuset *task_cs(struct task_struct *task)
 {
-	return css_cs(task_css(task, cpuset_subsys_id));
+	return css_cs(task_css(task, cpuset_cgrp_id));
 }
 
 static inline struct cpuset *parent_cs(struct cpuset *cs)
@@ -1521,7 +1521,7 @@ static void cpuset_attach(struct cgroup_subsys_state *css,
 	struct task_struct *task;
 	struct task_struct *leader = cgroup_taskset_first(tset);
 	struct cgroup_subsys_state *oldcss = cgroup_taskset_cur_css(tset,
-							cpuset_subsys_id);
+							cpuset_cgrp_id);
 	struct cpuset *cs = css_cs(css);
 	struct cpuset *oldcs = css_cs(oldcss);
 	struct cpuset *cpus_cs = effective_cpumask_cpuset(cs);
@@ -2024,8 +2024,7 @@ static void cpuset_css_free(struct cgroup_subsys_state *css)
 	kfree(cs);
 }
 
-struct cgroup_subsys cpuset_subsys = {
-	.name = "cpuset",
+struct cgroup_subsys cpuset_cgrp_subsys = {
 	.css_alloc = cpuset_css_alloc,
 	.css_online = cpuset_css_online,
 	.css_offline = cpuset_css_offline,
@@ -2033,7 +2032,6 @@ struct cgroup_subsys cpuset_subsys = {
 	.can_attach = cpuset_can_attach,
 	.cancel_attach = cpuset_cancel_attach,
 	.attach = cpuset_attach,
-	.subsys_id = cpuset_subsys_id,
 	.base_cftypes = files,
 	.early_init = 1,
 };
@@ -2699,7 +2697,7 @@ int proc_cpuset_show(struct seq_file *m, void *unused_v)
 		goto out_free;
 
 	rcu_read_lock();
-	css = task_css(tsk, cpuset_subsys_id);
+	css = task_css(tsk, cpuset_cgrp_id);
 	retval = cgroup_path(css->cgroup, buf, PAGE_SIZE);
 	rcu_read_unlock();
 	if (retval < 0)
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 56003c6..6490373 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -342,7 +342,7 @@ struct perf_cgroup {
 static inline struct perf_cgroup *
 perf_cgroup_from_task(struct task_struct *task)
 {
-	return container_of(task_css(task, perf_subsys_id),
+	return container_of(task_css(task, perf_event_cgrp_id),
 			    struct perf_cgroup, css);
 }
 
@@ -595,7 +595,7 @@ static inline int perf_cgroup_connect(int fd, struct perf_event *event,
 
 	rcu_read_lock();
 
-	css = css_from_dir(f.file->f_dentry, &perf_subsys);
+	css = css_from_dir(f.file->f_dentry, &perf_event_cgrp_subsys);
 	if (IS_ERR(css)) {
 		ret = PTR_ERR(css);
 		goto out;
@@ -8055,9 +8055,7 @@ static void perf_cgroup_exit(struct cgroup_subsys_state *css,
 	task_function_call(task, __perf_cgroup_move, task);
 }
 
-struct cgroup_subsys perf_subsys = {
-	.name		= "perf_event",
-	.subsys_id	= perf_subsys_id,
+struct cgroup_subsys perf_event_cgrp_subsys = {
 	.css_alloc	= perf_cgroup_css_alloc,
 	.css_free	= perf_cgroup_css_free,
 	.exit		= perf_cgroup_exit,
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index b46131e..d4cfc55 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7176,7 +7176,7 @@ void sched_move_task(struct task_struct *tsk)
 	if (unlikely(running))
 		tsk->sched_class->put_prev_task(rq, tsk);
 
-	tg = container_of(task_css_check(tsk, cpu_cgroup_subsys_id,
+	tg = container_of(task_css_check(tsk, cpu_cgrp_id,
 				lockdep_is_held(&tsk->sighand->siglock)),
 			  struct task_group, css);
 	tg = autogroup_task_group(tsk, tg);
@@ -7957,8 +7957,7 @@ static struct cftype cpu_files[] = {
 	{ }	/* terminate */
 };
 
-struct cgroup_subsys cpu_cgroup_subsys = {
-	.name		= "cpu",
+struct cgroup_subsys cpu_cgrp_subsys = {
 	.css_alloc	= cpu_cgroup_css_alloc,
 	.css_free	= cpu_cgroup_css_free,
 	.css_online	= cpu_cgroup_css_online,
@@ -7966,7 +7965,6 @@ struct cgroup_subsys cpu_cgroup_subsys = {
 	.can_attach	= cpu_cgroup_can_attach,
 	.attach		= cpu_cgroup_attach,
 	.exit		= cpu_cgroup_exit,
-	.subsys_id	= cpu_cgroup_subsys_id,
 	.base_cftypes	= cpu_files,
 	.early_init	= 1,
 };
diff --git a/kernel/sched/cpuacct.c b/kernel/sched/cpuacct.c
index 622e081..c143ee3 100644
--- a/kernel/sched/cpuacct.c
+++ b/kernel/sched/cpuacct.c
@@ -41,7 +41,7 @@ static inline struct cpuacct *css_ca(struct cgroup_subsys_state *css)
 /* return cpu accounting group to which this task belongs */
 static inline struct cpuacct *task_ca(struct task_struct *tsk)
 {
-	return css_ca(task_css(tsk, cpuacct_subsys_id));
+	return css_ca(task_css(tsk, cpuacct_cgrp_id));
 }
 
 static inline struct cpuacct *parent_ca(struct cpuacct *ca)
@@ -275,11 +275,9 @@ void cpuacct_account_field(struct task_struct *p, int index, u64 val)
 	rcu_read_unlock();
 }
 
-struct cgroup_subsys cpuacct_subsys = {
-	.name		= "cpuacct",
+struct cgroup_subsys cpuacct_cgrp_subsys = {
 	.css_alloc	= cpuacct_css_alloc,
 	.css_free	= cpuacct_css_free,
-	.subsys_id	= cpuacct_subsys_id,
 	.base_cftypes	= files,
 	.early_init	= 1,
 };