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, 10 insertions, 12 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 53385cd4e6f0..04a97bce2270 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -66,8 +66,8 @@
 
 #include <trace/events/vmscan.h>
 
-struct cgroup_subsys mem_cgroup_subsys __read_mostly;
-EXPORT_SYMBOL(mem_cgroup_subsys);
+struct cgroup_subsys memory_cgrp_subsys __read_mostly;
+EXPORT_SYMBOL(memory_cgrp_subsys);
 
 #define MEM_CGROUP_RECLAIM_RETRIES      5
 static struct mem_cgroup *root_mem_cgroup __read_mostly;
@@ -538,7 +538,7 @@ static inline struct mem_cgroup *mem_cgroup_from_id(unsigned short id)
 {
         struct cgroup_subsys_state *css;
 
-        css = css_from_id(id - 1, &mem_cgroup_subsys);
+        css = css_from_id(id - 1, &memory_cgrp_subsys);
         return mem_cgroup_from_css(css);
 }
 
@@ -1072,7 +1072,7 @@ struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p)
         if (unlikely(!p))
                 return NULL;
 
-        return mem_cgroup_from_css(task_css(p, mem_cgroup_subsys_id));
+        return mem_cgroup_from_css(task_css(p, memory_cgrp_id));
 }
 
 struct mem_cgroup *try_get_mem_cgroup_from_mm(struct mm_struct *mm)
@@ -1702,7 +1702,7 @@ void mem_cgroup_print_oom_info(struct mem_cgroup *memcg, struct task_struct *p)
         rcu_read_lock();
 
         mem_cgrp = memcg->css.cgroup;
-        task_cgrp = task_cgroup(p, mem_cgroup_subsys_id);
+        task_cgrp = task_cgroup(p, memory_cgrp_id);
 
         ret = cgroup_path(task_cgrp, memcg_name, PATH_MAX);
         if (ret < 0) {
@@ -6187,7 +6187,7 @@ static int memcg_write_event_control(struct cgroup_subsys_state *css,
 
         ret = -EINVAL;
         cfile_css = css_from_dir(cfile.file->f_dentry->d_parent,
-                                 &mem_cgroup_subsys);
+                                 &memory_cgrp_subsys);
         if (cfile_css == css && css_tryget(css))
                 ret = 0;
 
@@ -6566,11 +6566,11 @@ mem_cgroup_css_online(struct cgroup_subsys_state *css)
                  * unfortunate state in our controller.
                  */
                 if (parent != root_mem_cgroup)
-                        mem_cgroup_subsys.broken_hierarchy = true;
+                        memory_cgrp_subsys.broken_hierarchy = true;
         }
         mutex_unlock(&memcg_create_mutex);
 
-        return memcg_init_kmem(memcg, &mem_cgroup_subsys);
+        return memcg_init_kmem(memcg, &memory_cgrp_subsys);
 }
 
 /*
@@ -7264,9 +7264,7 @@ static void mem_cgroup_bind(struct cgroup_subsys_state *root_css)
                 mem_cgroup_from_css(root_css)->use_hierarchy = true;
 }
 
-struct cgroup_subsys mem_cgroup_subsys = {
-        .name = "memory",
-        .subsys_id = mem_cgroup_subsys_id,
+struct cgroup_subsys memory_cgrp_subsys = {
         .css_alloc = mem_cgroup_css_alloc,
         .css_online = mem_cgroup_css_online,
         .css_offline = mem_cgroup_css_offline,
@@ -7292,7 +7290,7 @@ __setup("swapaccount=", enable_swap_account);
 
 static void __init memsw_file_init(void)
 {
-        WARN_ON(cgroup_add_cftypes(&mem_cgroup_subsys, memsw_cgroup_files));
+        WARN_ON(cgroup_add_cftypes(&memory_cgrp_subsys, memsw_cgroup_files));
 }
 
 static void __init enable_swap_cgroup(void)