4 files changed, 78 insertions, 12 deletions

diff --git a/Documentation/cgroups/unified-hierarchy.txt b/Documentation/cgroups/unified-hierarchy.txt
index a7a2205539a7..4f4563277864 100644
--- a/Documentation/cgroups/unified-hierarchy.txt
+++ b/Documentation/cgroups/unified-hierarchy.txt
@@ -94,12 +94,18 @@ change soon.
 
  mount -t cgroup -o __DEVEL__sane_behavior cgroup $MOUNT_POINT
 
-All controllers which are not bound to other hierarchies are
-automatically bound to unified hierarchy and show up at the root of
-it.  Controllers which are enabled only in the root of unified
-hierarchy can be bound to other hierarchies.  This allows mixing
-unified hierarchy with the traditional multiple hierarchies in a fully
-backward compatible way.
+All controllers which support the unified hierarchy and are not bound
+to other hierarchies are automatically bound to unified hierarchy and
+show up at the root of it.  Controllers which are enabled only in the
+root of unified hierarchy can be bound to other hierarchies.  This
+allows mixing unified hierarchy with the traditional multiple
+hierarchies in a fully backward compatible way.
+
+For development purposes, the following boot parameter makes all
+controllers to appear on the unified hierarchy whether supported or
+not.
+
+ cgroup__DEVEL__legacy_files_on_dfl
 
 A controller can be moved across hierarchies only after the controller
 is no longer referenced in its current hierarchy.  Because per-cgroup
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index f5f0feef2701..9f76236ac158 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -590,6 +590,7 @@ static inline void pr_cont_cgroup_path(struct cgroup *cgrp)
 
 char *task_cgroup_path(struct task_struct *task, char *buf, size_t buflen);
 
+int cgroup_add_dfl_cftypes(struct cgroup_subsys *ss, struct cftype *cfts);
 int cgroup_add_legacy_cftypes(struct cgroup_subsys *ss, struct cftype *cfts);
 int cgroup_rm_cftypes(struct cftype *cfts);
 
@@ -671,8 +672,12 @@ struct cgroup_subsys {
          */
         struct list_head cfts;
 
-        /* base cftypes, automatically registered with subsys itself */
-        struct cftype *legacy_cftypes;  /* used on the legacy hierarchies */
+        /*
+         * Base cftypes which are automatically registered.  The two can
+         * point to the same array.
+         */
+        struct cftype *dfl_cftypes;     /* for the default hierarchy */
+        struct cftype *legacy_cftypes;  /* for the legacy hierarchies */
 
         /*
          * A subsystem may depend on other subsystems.  When such subsystem
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index c275aa439a6f..374ebdf74f35 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -149,6 +149,12 @@ struct cgroup_root cgrp_dfl_root;
  */
 static bool cgrp_dfl_root_visible;
 
+/*
+ * Set by the boot param of the same name and makes subsystems with NULL
+ * ->dfl_files to use ->legacy_files on the default hierarchy.
+ */
+static bool cgroup_legacy_files_on_dfl;
+
 /* some controllers are not supported in the default hierarchy */
 static const unsigned int cgrp_dfl_root_inhibit_ss_mask = 0
 #ifdef CONFIG_CGROUP_DEBUG
@@ -3085,6 +3091,9 @@ static void cgroup_exit_cftypes(struct cftype *cfts)
                         kfree(cft->kf_ops);
                 cft->kf_ops = NULL;
                 cft->ss = NULL;
+
+                /* revert flags set by cgroup core while adding @cfts */
+                cft->flags &= ~(CFTYPE_ONLY_ON_DFL | CFTYPE_INSANE);
         }
 }
 
@@ -3195,8 +3204,37 @@ static int cgroup_add_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
         return ret;
 }
 
+/**
+ * cgroup_add_dfl_cftypes - add an array of cftypes for default hierarchy
+ * @ss: target cgroup subsystem
+ * @cfts: zero-length name terminated array of cftypes
+ *
+ * Similar to cgroup_add_cftypes() but the added files are only used for
+ * the default hierarchy.
+ */
+int cgroup_add_dfl_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
+{
+        struct cftype *cft;
+
+        for (cft = cfts; cft && cft->name[0] != '\0'; cft++)
+                cft->flags |= CFTYPE_ONLY_ON_DFL;
+        return cgroup_add_cftypes(ss, cfts);
+}
+
+/**
+ * cgroup_add_legacy_cftypes - add an array of cftypes for legacy hierarchies
+ * @ss: target cgroup subsystem
+ * @cfts: zero-length name terminated array of cftypes
+ *
+ * Similar to cgroup_add_cftypes() but the added files are only used for
+ * the legacy hierarchies.
+ */
 int cgroup_add_legacy_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
 {
+        struct cftype *cft;
+
+        for (cft = cfts; cft && cft->name[0] != '\0'; cft++)
+                cft->flags |= CFTYPE_INSANE;
         return cgroup_add_cftypes(ss, cfts);
 }
 
@@ -4893,9 +4931,19 @@ int __init cgroup_init(void)
                  * disabled flag and cftype registration needs kmalloc,
                  * both of which aren't available during early_init.
                  */
-                if (!ss->disabled) {
-                        cgrp_dfl_root.subsys_mask |= 1 << ss->id;
-                        WARN_ON(cgroup_add_cftypes(ss, ss->legacy_cftypes));
+                if (ss->disabled)
+                        continue;
+
+                cgrp_dfl_root.subsys_mask |= 1 << ss->id;
+
+                if (cgroup_legacy_files_on_dfl && !ss->dfl_cftypes)
+                        ss->dfl_cftypes = ss->legacy_cftypes;
+
+                if (ss->dfl_cftypes == ss->legacy_cftypes) {
+                        WARN_ON(cgroup_add_cftypes(ss, ss->dfl_cftypes));
+                } else {
+                        WARN_ON(cgroup_add_dfl_cftypes(ss, ss->dfl_cftypes));
+                        WARN_ON(cgroup_add_legacy_cftypes(ss, ss->legacy_cftypes));
                 }
         }
 
@@ -5291,6 +5339,14 @@ static int __init cgroup_disable(char *str)
 }
 __setup("cgroup_disable=", cgroup_disable);
 
+static int __init cgroup_set_legacy_files_on_dfl(char *str)
+{
+        printk("cgroup: using legacy files on the default hierarchy\n");
+        cgroup_legacy_files_on_dfl = true;
+        return 0;
+}
+__setup("cgroup__DEVEL__legacy_files_on_dfl", cgroup_set_legacy_files_on_dfl);
+
 /**
  * css_tryget_online_from_dir - get corresponding css from a cgroup dentry
  * @dentry: directory dentry of interest
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index b6b3c6fea509..45c10c6fc3ce 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -6003,7 +6003,6 @@ static struct cftype mem_cgroup_files[] = {
         },
         {
                 .name = "use_hierarchy",
-                .flags = CFTYPE_INSANE,
                 .write_u64 = mem_cgroup_hierarchy_write,
                 .read_u64 = mem_cgroup_hierarchy_read,
         },