tracing: Adjust conditional expression latency formatting.
[linux-2.6.git] / kernel / cgroup.c
index 4ca928d..95362d1 100644 (file)
@@ -52,7 +52,6 @@
 #include <linux/cgroupstats.h>
 #include <linux/hash.h>
 #include <linux/namei.h>
-#include <linux/smp_lock.h>
 #include <linux/pid_namespace.h>
 #include <linux/idr.h>
 #include <linux/vmalloc.h> /* TODO: replace with more sophisticated array */
@@ -138,7 +137,7 @@ struct css_id {
         * is called after synchronize_rcu(). But for safe use, css_is_removed()
         * css_tryget() should be used for avoiding race.
         */
-       struct cgroup_subsys_state *css;
+       struct cgroup_subsys_state __rcu *css;
        /*
         * ID of this css.
         */
@@ -244,6 +243,11 @@ static int notify_on_release(const struct cgroup *cgrp)
        return test_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
 }
 
+static int clone_children(const struct cgroup *cgrp)
+{
+       return test_bit(CGRP_CLONE_CHILDREN, &cgrp->flags);
+}
+
 /*
  * for_each_subsys() allows you to iterate on each subsystem attached to
  * an active hierarchy
@@ -760,6 +764,7 @@ EXPORT_SYMBOL_GPL(cgroup_unlock);
  */
 
 static int cgroup_mkdir(struct inode *dir, struct dentry *dentry, int mode);
+static struct dentry *cgroup_lookup(struct inode *, struct dentry *, struct nameidata *);
 static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry);
 static int cgroup_populate_dir(struct cgroup *cgrp);
 static const struct inode_operations cgroup_dir_inode_operations;
@@ -778,6 +783,7 @@ static struct inode *cgroup_new_inode(mode_t mode, struct super_block *sb)
        struct inode *inode = new_inode(sb);
 
        if (inode) {
+               inode->i_ino = get_next_ino();
                inode->i_mode = mode;
                inode->i_uid = current_fsuid();
                inode->i_gid = current_fsgid();
@@ -855,6 +861,11 @@ static void cgroup_diput(struct dentry *dentry, struct inode *inode)
        iput(inode);
 }
 
+static int cgroup_delete(const struct dentry *d)
+{
+       return 1;
+}
+
 static void remove_dir(struct dentry *d)
 {
        struct dentry *parent = dget(d->d_parent);
@@ -869,25 +880,29 @@ static void cgroup_clear_directory(struct dentry *dentry)
        struct list_head *node;
 
        BUG_ON(!mutex_is_locked(&dentry->d_inode->i_mutex));
-       spin_lock(&dcache_lock);
+       spin_lock(&dentry->d_lock);
        node = dentry->d_subdirs.next;
        while (node != &dentry->d_subdirs) {
                struct dentry *d = list_entry(node, struct dentry, d_u.d_child);
+
+               spin_lock_nested(&d->d_lock, DENTRY_D_LOCK_NESTED);
                list_del_init(node);
                if (d->d_inode) {
                        /* This should never be called on a cgroup
                         * directory with child cgroups */
                        BUG_ON(d->d_inode->i_mode & S_IFDIR);
-                       d = dget_locked(d);
-                       spin_unlock(&dcache_lock);
+                       dget_dlock(d);
+                       spin_unlock(&d->d_lock);
+                       spin_unlock(&dentry->d_lock);
                        d_delete(d);
                        simple_unlink(dentry->d_inode, d);
                        dput(d);
-                       spin_lock(&dcache_lock);
-               }
+                       spin_lock(&dentry->d_lock);
+               } else
+                       spin_unlock(&d->d_lock);
                node = dentry->d_subdirs.next;
        }
-       spin_unlock(&dcache_lock);
+       spin_unlock(&dentry->d_lock);
 }
 
 /*
@@ -895,11 +910,16 @@ static void cgroup_clear_directory(struct dentry *dentry)
  */
 static void cgroup_d_remove_dir(struct dentry *dentry)
 {
+       struct dentry *parent;
+
        cgroup_clear_directory(dentry);
 
-       spin_lock(&dcache_lock);
+       parent = dentry->d_parent;
+       spin_lock(&parent->d_lock);
+       spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
        list_del_init(&dentry->d_u.d_child);
-       spin_unlock(&dcache_lock);
+       spin_unlock(&dentry->d_lock);
+       spin_unlock(&parent->d_lock);
        remove_dir(dentry);
 }
 
@@ -1040,6 +1060,8 @@ static int cgroup_show_options(struct seq_file *seq, struct vfsmount *vfs)
                seq_puts(seq, ",noprefix");
        if (strlen(root->release_agent_path))
                seq_printf(seq, ",release_agent=%s", root->release_agent_path);
+       if (clone_children(&root->top_cgroup))
+               seq_puts(seq, ",clone_children");
        if (strlen(root->name))
                seq_printf(seq, ",name=%s", root->name);
        mutex_unlock(&cgroup_mutex);
@@ -1050,6 +1072,7 @@ struct cgroup_sb_opts {
        unsigned long subsys_bits;
        unsigned long flags;
        char *release_agent;
+       bool clone_children;
        char *name;
        /* User explicitly requested empty subsystem */
        bool none;
@@ -1066,7 +1089,8 @@ struct cgroup_sb_opts {
  */
 static int parse_cgroupfs_options(char *data, struct cgroup_sb_opts *opts)
 {
-       char *token, *o = data ?: "all";
+       char *token, *o = data;
+       bool all_ss = false, one_ss = false;
        unsigned long mask = (unsigned long)-1;
        int i;
        bool module_pin_failed = false;
@@ -1082,30 +1106,37 @@ static int parse_cgroupfs_options(char *data, struct cgroup_sb_opts *opts)
        while ((token = strsep(&o, ",")) != NULL) {
                if (!*token)
                        return -EINVAL;
-               if (!strcmp(token, "all")) {
-                       /* Add all non-disabled subsystems */
-                       opts->subsys_bits = 0;
-                       for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
-                               struct cgroup_subsys *ss = subsys[i];
-                               if (ss == NULL)
-                                       continue;
-                               if (!ss->disabled)
-                                       opts->subsys_bits |= 1ul << i;
-                       }
-               } else if (!strcmp(token, "none")) {
+               if (!strcmp(token, "none")) {
                        /* Explicitly have no subsystems */
                        opts->none = true;
-               } else if (!strcmp(token, "noprefix")) {
+                       continue;
+               }
+               if (!strcmp(token, "all")) {
+                       /* Mutually exclusive option 'all' + subsystem name */
+                       if (one_ss)
+                               return -EINVAL;
+                       all_ss = true;
+                       continue;
+               }
+               if (!strcmp(token, "noprefix")) {
                        set_bit(ROOT_NOPREFIX, &opts->flags);
-               } else if (!strncmp(token, "release_agent=", 14)) {
+                       continue;
+               }
+               if (!strcmp(token, "clone_children")) {
+                       opts->clone_children = true;
+                       continue;
+               }
+               if (!strncmp(token, "release_agent=", 14)) {
                        /* Specifying two release agents is forbidden */
                        if (opts->release_agent)
                                return -EINVAL;
                        opts->release_agent =
-                               kstrndup(token + 14, PATH_MAX, GFP_KERNEL);
+                               kstrndup(token + 14, PATH_MAX - 1, GFP_KERNEL);
                        if (!opts->release_agent)
                                return -ENOMEM;
-               } else if (!strncmp(token, "name=", 5)) {
+                       continue;
+               }
+               if (!strncmp(token, "name=", 5)) {
                        const char *name = token + 5;
                        /* Can't specify an empty name */
                        if (!strlen(name))
@@ -1123,24 +1154,48 @@ static int parse_cgroupfs_options(char *data, struct cgroup_sb_opts *opts)
                        if (opts->name)
                                return -EINVAL;
                        opts->name = kstrndup(name,
-                                             MAX_CGROUP_ROOT_NAMELEN,
+                                             MAX_CGROUP_ROOT_NAMELEN - 1,
                                              GFP_KERNEL);
                        if (!opts->name)
                                return -ENOMEM;
-               } else {
-                       struct cgroup_subsys *ss;
-                       for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
-                               ss = subsys[i];
-                               if (ss == NULL)
-                                       continue;
-                               if (!strcmp(token, ss->name)) {
-                                       if (!ss->disabled)
-                                               set_bit(i, &opts->subsys_bits);
-                                       break;
-                               }
-                       }
-                       if (i == CGROUP_SUBSYS_COUNT)
-                               return -ENOENT;
+
+                       continue;
+               }
+
+               for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
+                       struct cgroup_subsys *ss = subsys[i];
+                       if (ss == NULL)
+                               continue;
+                       if (strcmp(token, ss->name))
+                               continue;
+                       if (ss->disabled)
+                               continue;
+
+                       /* Mutually exclusive option 'all' + subsystem name */
+                       if (all_ss)
+                               return -EINVAL;
+                       set_bit(i, &opts->subsys_bits);
+                       one_ss = true;
+
+                       break;
+               }
+               if (i == CGROUP_SUBSYS_COUNT)
+                       return -ENOENT;
+       }
+
+       /*
+        * If the 'all' option was specified select all the subsystems,
+        * otherwise 'all, 'none' and a subsystem name options were not
+        * specified, let's default to 'all'
+        */
+       if (all_ss || (!all_ss && !one_ss && !opts->none)) {
+               for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
+                       struct cgroup_subsys *ss = subsys[i];
+                       if (ss == NULL)
+                               continue;
+                       if (ss->disabled)
+                               continue;
+                       set_bit(i, &opts->subsys_bits);
                }
        }
 
@@ -1222,7 +1277,6 @@ static int cgroup_remount(struct super_block *sb, int *flags, char *data)
        struct cgroup *cgrp = &root->top_cgroup;
        struct cgroup_sb_opts opts;
 
-       lock_kernel();
        mutex_lock(&cgrp->dentry->d_inode->i_mutex);
        mutex_lock(&cgroup_mutex);
 
@@ -1255,7 +1309,6 @@ static int cgroup_remount(struct super_block *sb, int *flags, char *data)
        kfree(opts.name);
        mutex_unlock(&cgroup_mutex);
        mutex_unlock(&cgrp->dentry->d_inode->i_mutex);
-       unlock_kernel();
        return ret;
 }
 
@@ -1357,6 +1410,8 @@ static struct cgroupfs_root *cgroup_root_from_opts(struct cgroup_sb_opts *opts)
                strcpy(root->release_agent_path, opts->release_agent);
        if (opts->name)
                strcpy(root->name, opts->name);
+       if (opts->clone_children)
+               set_bit(CGRP_CLONE_CHILDREN, &root->top_cgroup.flags);
        return root;
 }
 
@@ -1400,6 +1455,11 @@ static int cgroup_set_super(struct super_block *sb, void *data)
 
 static int cgroup_get_rootdir(struct super_block *sb)
 {
+       static const struct dentry_operations cgroup_dops = {
+               .d_iput = cgroup_diput,
+               .d_delete = cgroup_delete,
+       };
+
        struct inode *inode =
                cgroup_new_inode(S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR, sb);
        struct dentry *dentry;
@@ -1417,12 +1477,14 @@ static int cgroup_get_rootdir(struct super_block *sb)
                return -ENOMEM;
        }
        sb->s_root = dentry;
+       /* for everything else we want ->d_op set */
+       sb->s_d_op = &cgroup_dops;
        return 0;
 }
 
-static int cgroup_get_sb(struct file_system_type *fs_type,
+static struct dentry *cgroup_mount(struct file_system_type *fs_type,
                         int flags, const char *unused_dev_name,
-                        void *data, struct vfsmount *mnt)
+                        void *data)
 {
        struct cgroup_sb_opts opts;
        struct cgroupfs_root *root;
@@ -1556,10 +1618,9 @@ static int cgroup_get_sb(struct file_system_type *fs_type,
                drop_parsed_module_refcounts(opts.subsys_bits);
        }
 
-       simple_set_mnt(mnt, sb);
        kfree(opts.release_agent);
        kfree(opts.name);
-       return 0;
+       return dget(sb->s_root);
 
  drop_new_super:
        deactivate_locked_super(sb);
@@ -1568,8 +1629,7 @@ static int cgroup_get_sb(struct file_system_type *fs_type,
  out_err:
        kfree(opts.release_agent);
        kfree(opts.name);
-
-       return ret;
+       return ERR_PTR(ret);
 }
 
 static void cgroup_kill_sb(struct super_block *sb) {
@@ -1619,10 +1679,12 @@ static void cgroup_kill_sb(struct super_block *sb) {
 
 static struct file_system_type cgroup_fs_type = {
        .name = "cgroup",
-       .get_sb = cgroup_get_sb,
+       .mount = cgroup_mount,
        .kill_sb = cgroup_kill_sb,
 };
 
+static struct kobject *cgroup_kobj;
+
 static inline struct cgroup *__d_cgrp(struct dentry *dentry)
 {
        return dentry->d_fsdata;
@@ -1788,6 +1850,30 @@ out:
        return retval;
 }
 
+/**
+ * cgroup_attach_task_all - attach task 'tsk' to all cgroups of task 'from'
+ * @from: attach to all cgroups of a given task
+ * @tsk: the task to be attached
+ */
+int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk)
+{
+       struct cgroupfs_root *root;
+       int retval = 0;
+
+       cgroup_lock();
+       for_each_active_root(root) {
+               struct cgroup *from_cg = task_cgroup_from_root(from, root);
+
+               retval = cgroup_attach_task(from_cg, tsk);
+               if (retval)
+                       break;
+       }
+       cgroup_unlock();
+
+       return retval;
+}
+EXPORT_SYMBOL_GPL(cgroup_attach_task_all);
+
 /*
  * Attach task with pid 'pid' to cgroup 'cgrp'. Call with cgroup_mutex
  * held. May take task_lock of task
@@ -1857,6 +1943,8 @@ static int cgroup_release_agent_write(struct cgroup *cgrp, struct cftype *cft,
                                      const char *buffer)
 {
        BUILD_BUG_ON(sizeof(cgrp->root->release_agent_path) < PATH_MAX);
+       if (strlen(buffer) >= PATH_MAX)
+               return -EINVAL;
        if (!cgroup_lock_live_group(cgrp))
                return -ENODEV;
        strcpy(cgrp->root->release_agent_path, buffer);
@@ -2114,12 +2202,20 @@ static const struct file_operations cgroup_file_operations = {
 };
 
 static const struct inode_operations cgroup_dir_inode_operations = {
-       .lookup = simple_lookup,
+       .lookup = cgroup_lookup,
        .mkdir = cgroup_mkdir,
        .rmdir = cgroup_rmdir,
        .rename = cgroup_rename,
 };
 
+static struct dentry *cgroup_lookup(struct inode *dir, struct dentry *dentry, struct nameidata *nd)
+{
+       if (dentry->d_name.len > NAME_MAX)
+               return ERR_PTR(-ENAMETOOLONG);
+       d_add(dentry, NULL);
+       return NULL;
+}
+
 /*
  * Check if a file is a control file
  */
@@ -2133,10 +2229,6 @@ static inline struct cftype *__file_cft(struct file *file)
 static int cgroup_create_file(struct dentry *dentry, mode_t mode,
                                struct super_block *sb)
 {
-       static const struct dentry_operations cgroup_dops = {
-               .d_iput = cgroup_diput,
-       };
-
        struct inode *inode;
 
        if (!dentry)
@@ -2162,7 +2254,6 @@ static int cgroup_create_file(struct dentry *dentry, mode_t mode,
                inode->i_size = 0;
                inode->i_fop = &cgroup_file_operations;
        }
-       dentry->d_op = &cgroup_dops;
        d_instantiate(dentry, inode);
        dget(dentry);   /* Extra count - pin the dentry in core */
        return 0;
@@ -2994,7 +3085,6 @@ static void cgroup_event_remove(struct work_struct *work)
                        remove);
        struct cgroup *cgrp = event->cgrp;
 
-       /* TODO: check return code */
        event->cft->unregister_event(cgrp, event->cft, event->eventfd);
 
        eventfd_ctx_put(event->eventfd);
@@ -3016,7 +3106,7 @@ static int cgroup_event_wake(wait_queue_t *wait, unsigned mode,
        unsigned long flags = (unsigned long)key;
 
        if (flags & POLLHUP) {
-               remove_wait_queue_locked(event->wqh, &event->wait);
+               __remove_wait_queue(event->wqh, &event->wait);
                spin_lock(&cgrp->event_list_lock);
                list_del(&event->list);
                spin_unlock(&cgrp->event_list_lock);
@@ -3151,6 +3241,23 @@ fail:
        return ret;
 }
 
+static u64 cgroup_clone_children_read(struct cgroup *cgrp,
+                                   struct cftype *cft)
+{
+       return clone_children(cgrp);
+}
+
+static int cgroup_clone_children_write(struct cgroup *cgrp,
+                                    struct cftype *cft,
+                                    u64 val)
+{
+       if (val)
+               set_bit(CGRP_CLONE_CHILDREN, &cgrp->flags);
+       else
+               clear_bit(CGRP_CLONE_CHILDREN, &cgrp->flags);
+       return 0;
+}
+
 /*
  * for the common functions, 'private' gives the type of file
  */
@@ -3181,6 +3288,11 @@ static struct cftype files[] = {
                .write_string = cgroup_write_event_control,
                .mode = S_IWUGO,
        },
+       {
+               .name = "cgroup.clone_children",
+               .read_u64 = cgroup_clone_children_read,
+               .write_u64 = cgroup_clone_children_write,
+       },
 };
 
 static struct cftype cft_release_agent = {
@@ -3310,6 +3422,9 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
        if (notify_on_release(parent))
                set_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
 
+       if (clone_children(parent))
+               set_bit(CGRP_CLONE_CHILDREN, &cgrp->flags);
+
        for_each_subsys(root, ss) {
                struct cgroup_subsys_state *css = ss->create(ss, cgrp);
 
@@ -3324,6 +3439,8 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
                                goto err_destroy;
                }
                /* At error, ->destroy() callback has to free assigned ID. */
+               if (clone_children(parent) && ss->post_clone)
+                       ss->post_clone(ss, cgrp);
        }
 
        cgroup_lock_hierarchy(root);
@@ -3546,9 +3663,7 @@ again:
        list_del(&cgrp->sibling);
        cgroup_unlock_hierarchy(cgrp->root);
 
-       spin_lock(&cgrp->dentry->d_lock);
        d = dget(cgrp->dentry);
-       spin_unlock(&d->d_lock);
 
        cgroup_d_remove_dir(d);
        dput(d);
@@ -3615,7 +3730,7 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss)
  * @ss: the subsystem to load
  *
  * This function should be called in a modular subsystem's initcall. If the
- * subsytem is built as a module, it will be assigned a new subsys_id and set
+ * subsystem is built as a module, it will be assigned a new subsys_id and set
  * up for use. If the subsystem is built-in anyway, work is delegated to the
  * simpler cgroup_init_subsys.
  */
@@ -3872,9 +3987,18 @@ int __init cgroup_init(void)
        hhead = css_set_hash(init_css_set.subsys);
        hlist_add_head(&init_css_set.hlist, hhead);
        BUG_ON(!init_root_id(&rootnode));
+
+       cgroup_kobj = kobject_create_and_add("cgroup", fs_kobj);
+       if (!cgroup_kobj) {
+               err = -ENOMEM;
+               goto out;
+       }
+
        err = register_filesystem(&cgroup_fs_type);
-       if (err < 0)
+       if (err < 0) {
+               kobject_put(cgroup_kobj);
                goto out;
+       }
 
        proc_create("cgroups", 0, NULL, &proc_cgroupstats_operations);
 
@@ -4106,20 +4230,8 @@ void cgroup_post_fork(struct task_struct *child)
  */
 void cgroup_exit(struct task_struct *tsk, int run_callbacks)
 {
-       int i;
        struct css_set *cg;
-
-       if (run_callbacks && need_forkexit_callback) {
-               /*
-                * modular subsystems can't use callbacks, so no need to lock
-                * the subsys array
-                */
-               for (i = 0; i < CGROUP_BUILTIN_SUBSYS_COUNT; i++) {
-                       struct cgroup_subsys *ss = subsys[i];
-                       if (ss->exit)
-                               ss->exit(ss, tsk);
-               }
-       }
+       int i;
 
        /*
         * Unlink from the css_set task list if necessary.
@@ -4137,7 +4249,24 @@ void cgroup_exit(struct task_struct *tsk, int run_callbacks)
        task_lock(tsk);
        cg = tsk->cgroups;
        tsk->cgroups = &init_css_set;
+
+       if (run_callbacks && need_forkexit_callback) {
+               /*
+                * modular subsystems can't use callbacks, so no need to lock
+                * the subsys array
+                */
+               for (i = 0; i < CGROUP_BUILTIN_SUBSYS_COUNT; i++) {
+                       struct cgroup_subsys *ss = subsys[i];
+                       if (ss->exit) {
+                               struct cgroup *old_cgrp =
+                                       rcu_dereference_raw(cg->subsys[i])->cgroup;
+                               struct cgroup *cgrp = task_cgroup(tsk, i);
+                               ss->exit(ss, cgrp, old_cgrp, tsk);
+                       }
+               }
+       }
        task_unlock(tsk);
+
        if (cg)
                put_css_set_taskexit(cg);
 }
@@ -4435,7 +4564,15 @@ __setup("cgroup_disable=", cgroup_disable);
  */
 unsigned short css_id(struct cgroup_subsys_state *css)
 {
-       struct css_id *cssid = rcu_dereference(css->id);
+       struct css_id *cssid;
+
+       /*
+        * This css_id() can return correct value when somone has refcnt
+        * on this or this is under rcu_read_lock(). Once css->id is allocated,
+        * it's unchanged until freed.
+        */
+       cssid = rcu_dereference_check(css->id,
+                       rcu_read_lock_held() || atomic_read(&css->refcnt));
 
        if (cssid)
                return cssid->id;
@@ -4445,7 +4582,10 @@ EXPORT_SYMBOL_GPL(css_id);
 
 unsigned short css_depth(struct cgroup_subsys_state *css)
 {
-       struct css_id *cssid = rcu_dereference(css->id);
+       struct css_id *cssid;
+
+       cssid = rcu_dereference_check(css->id,
+                       rcu_read_lock_held() || atomic_read(&css->refcnt));
 
        if (cssid)
                return cssid->depth;
@@ -4453,15 +4593,36 @@ unsigned short css_depth(struct cgroup_subsys_state *css)
 }
 EXPORT_SYMBOL_GPL(css_depth);
 
+/**
+ *  css_is_ancestor - test "root" css is an ancestor of "child"
+ * @child: the css to be tested.
+ * @root: the css supporsed to be an ancestor of the child.
+ *
+ * Returns true if "root" is an ancestor of "child" in its hierarchy. Because
+ * this function reads css->id, this use rcu_dereference() and rcu_read_lock().
+ * But, considering usual usage, the csses should be valid objects after test.
+ * Assuming that the caller will do some action to the child if this returns
+ * returns true, the caller must take "child";s reference count.
+ * If "child" is valid object and this returns true, "root" is valid, too.
+ */
+
 bool css_is_ancestor(struct cgroup_subsys_state *child,
                    const struct cgroup_subsys_state *root)
 {
-       struct css_id *child_id = rcu_dereference(child->id);
-       struct css_id *root_id = rcu_dereference(root->id);
+       struct css_id *child_id;
+       struct css_id *root_id;
+       bool ret = true;
 
-       if (!child_id || !root_id || (child_id->depth < root_id->depth))
-               return false;
-       return child_id->stack[root_id->depth] == root_id->id;
+       rcu_read_lock();
+       child_id  = rcu_dereference(child->id);
+       root_id = rcu_dereference(root->id);
+       if (!child_id
+           || !root_id
+           || (child_id->depth < root_id->depth)
+           || (child_id->stack[root_id->depth] != root_id->id))
+               ret = false;
+       rcu_read_unlock();
+       return ret;
 }
 
 static void __free_css_id_cb(struct rcu_head *head)
@@ -4561,13 +4722,13 @@ static int alloc_css_id(struct cgroup_subsys *ss, struct cgroup *parent,
 {
        int subsys_id, i, depth = 0;
        struct cgroup_subsys_state *parent_css, *child_css;
-       struct css_id *child_id, *parent_id = NULL;
+       struct css_id *child_id, *parent_id;
 
        subsys_id = ss->subsys_id;
        parent_css = parent->subsys[subsys_id];
        child_css = child->subsys[subsys_id];
-       depth = css_depth(parent_css) + 1;
        parent_id = parent_css->id;
+       depth = parent_id->depth + 1;
 
        child_id = get_new_cssid(ss, depth);
        if (IS_ERR(child_id))
@@ -4657,6 +4818,29 @@ css_get_next(struct cgroup_subsys *ss, int id,
        return ret;
 }
 
+/*
+ * get corresponding css from file open on cgroupfs directory
+ */
+struct cgroup_subsys_state *cgroup_css_from_dir(struct file *f, int id)
+{
+       struct cgroup *cgrp;
+       struct inode *inode;
+       struct cgroup_subsys_state *css;
+
+       inode = f->f_dentry->d_inode;
+       /* check in cgroup filesystem dir */
+       if (inode->i_op != &cgroup_dir_inode_operations)
+               return ERR_PTR(-EBADF);
+
+       if (id < 0 || id >= CGROUP_SUBSYS_COUNT)
+               return ERR_PTR(-EINVAL);
+
+       /* get cgroup */
+       cgrp = __d_cgrp(f->f_dentry);
+       css = cgrp->subsys[id];
+       return css ? css : ERR_PTR(-ENOENT);
+}
+
 #ifdef CONFIG_CGROUP_DEBUG
 static struct cgroup_subsys_state *debug_create(struct cgroup_subsys *ss,
                                                   struct cgroup *cont)