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>

1 files changed, 3 insertions, 5 deletions

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 56003c6edfd3..64903731d834 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,