cgroup: drop module support

With module supported dropped from net_prio, no controller is using
cgroup module support.  None of actual resource controllers can be
built as a module and we aren't gonna add new controllers which don't
control resources.  This patch drops module support from cgroup.

* cgroup_[un]load_subsys() and cgroup_subsys->module removed.

* As there's no point in distinguishing IS_BUILTIN() and IS_MODULE(),
  cgroup_subsys.h now uses IS_ENABLED() directly.

* enum cgroup_subsys_id now exactly matches the list of enabled
  controllers as ordered in cgroup_subsys.h.

* cgroup_subsys[] is now a contiguously occupied array.  Size
  specification is no longer necessary and dropped.

* for_each_builtin_subsys() is removed and for_each_subsys() is
  updated to not require any locking.

* module ref handling is removed from rebind_subsystems().

* Module related comments dropped.

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

v3: Added {} around the if (need_forkexit_callback) block in
    cgroup_post_fork() for readability as suggested by Li.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>

2 files changed, 0 insertions, 2 deletions

diff --git a/net/core/netclassid_cgroup.c b/net/core/netclassid_cgroup.c
index 9fc7f90d034c..9e5ad5d74e60 100644
--- a/net/core/netclassid_cgroup.c
+++ b/net/core/netclassid_cgroup.c
@@ -110,5 +110,4 @@ struct cgroup_subsys net_cls_subsys = {
         .attach                 = cgrp_attach,
         .subsys_id              = net_cls_subsys_id,
         .base_cftypes           = ss_files,
-        .module                 = THIS_MODULE,
 };
diff --git a/net/core/netprio_cgroup.c b/net/core/netprio_cgroup.c
index cc3a31e7dc08..857e1603f9b7 100644
--- a/net/core/netprio_cgroup.c
+++ b/net/core/netprio_cgroup.c
@@ -252,7 +252,6 @@ struct cgroup_subsys net_prio_subsys = {
         .attach         = net_prio_attach,
         .subsys_id      = net_prio_subsys_id,
         .base_cftypes   = ss_files,
-        .module         = THIS_MODULE,
 };
 
 static int netprio_device_event(struct notifier_block *unused,