*/
#include <linux/cgroup.h>
-#include <linux/module.h>
+#include <linux/cred.h>
#include <linux/ctype.h>
#include <linux/errno.h>
#include <linux/fs.h>
+#include <linux/init_task.h>
#include <linux/kernel.h>
#include <linux/list.h>
#include <linux/mm.h>
#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 */
#include <linux/eventfd.h>
#include <linux/poll.h>
+#include <linux/flex_array.h> /* used in cgroup_attach_proc */
-#include <asm/atomic.h>
+#include <linux/atomic.h>
static DEFINE_MUTEX(cgroup_mutex);
* 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.
*/
};
/*
- * cgroup_event represents events which userspace want to recieve.
+ * cgroup_event represents events which userspace want to receive.
*/
struct cgroup_event {
/*
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
return &css_set_table[index];
}
-static void free_css_set_rcu(struct rcu_head *obj)
-{
- struct css_set *cg = container_of(obj, struct css_set, rcu_head);
- kfree(cg);
-}
-
/* We don't maintain the lists running through each css_set to its
* task until after the first call to cgroup_iter_start(). This
* reduces the fork()/exit() overhead for people who have cgroups
}
write_unlock(&css_set_lock);
- call_rcu(&cg->rcu_head, free_css_set_rcu);
+ kfree_rcu(cg, rcu_head);
}
/*
*/
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;
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();
static int cgroup_call_pre_destroy(struct cgroup *cgrp)
{
struct cgroup_subsys *ss;
- struct cgroup_event *event, *tmp;
int ret = 0;
for_each_subsys(cgrp->root, ss)
if (ss->pre_destroy) {
ret = ss->pre_destroy(ss, cgrp);
if (ret)
- goto out;
+ break;
}
- /*
- * Unregister events and notify userspace.
- */
- spin_lock(&cgrp->event_list_lock);
- list_for_each_entry_safe(event, tmp, &cgrp->event_list, list) {
- list_del(&event->list);
- eventfd_signal(event->eventfd, 1);
- schedule_work(&event->remove);
- }
- spin_unlock(&cgrp->event_list_lock);
-
-out:
return ret;
}
-static void free_cgroup_rcu(struct rcu_head *obj)
-{
- struct cgroup *cgrp = container_of(obj, struct cgroup, rcu_head);
-
- kfree(cgrp);
-}
-
static void cgroup_diput(struct dentry *dentry, struct inode *inode)
{
/* is dentry a directory ? if so, kfree() associated cgroup */
*/
BUG_ON(!list_empty(&cgrp->pidlists));
- call_rcu(&cgrp->rcu_head, free_cgroup_rcu);
+ kfree_rcu(cgrp, rcu_head);
}
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);
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);
}
/*
*/
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);
}
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);
unsigned long subsys_bits;
unsigned long flags;
char *release_agent;
+ bool clone_children;
char *name;
/* User explicitly requested empty subsystem */
bool none;
*/
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;
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))
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);
}
}
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);
kfree(opts.name);
mutex_unlock(&cgroup_mutex);
mutex_unlock(&cgrp->dentry->d_inode->i_mutex);
- unlock_kernel();
return ret;
}
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;
}
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;
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;
struct cgroup *root_cgrp = &root->top_cgroup;
struct inode *inode;
struct cgroupfs_root *existing_root;
+ const struct cred *cred;
int i;
BUG_ON(sb->s_root != NULL);
BUG_ON(!list_empty(&root_cgrp->children));
BUG_ON(root->number_of_cgroups != 1);
+ cred = override_creds(&init_cred);
cgroup_populate_dir(root_cgrp);
+ revert_creds(cred);
mutex_unlock(&cgroup_mutex);
mutex_unlock(&inode->i_mutex);
} else {
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);
out_err:
kfree(opts.release_agent);
kfree(opts.name);
-
- return ret;
+ return ERR_PTR(ret);
}
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;
int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen)
{
char *start;
- struct dentry *dentry = rcu_dereference(cgrp->dentry);
+ struct dentry *dentry = rcu_dereference_check(cgrp->dentry,
+ cgroup_lock_is_held());
if (!dentry || cgrp == dummytop) {
/*
*--start = '\0';
for (;;) {
int len = dentry->d_name.len;
+
if ((start -= len) < buf)
return -ENAMETOOLONG;
- memcpy(start, cgrp->dentry->d_name.name, len);
+ memcpy(start, dentry->d_name.name, len);
cgrp = cgrp->parent;
if (!cgrp)
break;
- dentry = rcu_dereference(cgrp->dentry);
+
+ dentry = rcu_dereference_check(cgrp->dentry,
+ cgroup_lock_is_held());
if (!cgrp->parent)
continue;
if (--start < buf)
}
EXPORT_SYMBOL_GPL(cgroup_path);
+/*
+ * cgroup_task_migrate - move a task from one cgroup to another.
+ *
+ * 'guarantee' is set if the caller promises that a new css_set for the task
+ * will already exist. If not set, this function might sleep, and can fail with
+ * -ENOMEM. Otherwise, it can only fail with -ESRCH.
+ */
+static int cgroup_task_migrate(struct cgroup *cgrp, struct cgroup *oldcgrp,
+ struct task_struct *tsk, bool guarantee)
+{
+ struct css_set *oldcg;
+ struct css_set *newcg;
+
+ /*
+ * get old css_set. we need to take task_lock and refcount it, because
+ * an exiting task can change its css_set to init_css_set and drop its
+ * old one without taking cgroup_mutex.
+ */
+ task_lock(tsk);
+ oldcg = tsk->cgroups;
+ get_css_set(oldcg);
+ task_unlock(tsk);
+
+ /* locate or allocate a new css_set for this task. */
+ if (guarantee) {
+ /* we know the css_set we want already exists. */
+ struct cgroup_subsys_state *template[CGROUP_SUBSYS_COUNT];
+ read_lock(&css_set_lock);
+ newcg = find_existing_css_set(oldcg, cgrp, template);
+ BUG_ON(!newcg);
+ get_css_set(newcg);
+ read_unlock(&css_set_lock);
+ } else {
+ might_sleep();
+ /* find_css_set will give us newcg already referenced. */
+ newcg = find_css_set(oldcg, cgrp);
+ if (!newcg) {
+ put_css_set(oldcg);
+ return -ENOMEM;
+ }
+ }
+ put_css_set(oldcg);
+
+ /* if PF_EXITING is set, the tsk->cgroups pointer is no longer safe. */
+ task_lock(tsk);
+ if (tsk->flags & PF_EXITING) {
+ task_unlock(tsk);
+ put_css_set(newcg);
+ return -ESRCH;
+ }
+ rcu_assign_pointer(tsk->cgroups, newcg);
+ task_unlock(tsk);
+
+ /* Update the css_set linked lists if we're using them */
+ write_lock(&css_set_lock);
+ if (!list_empty(&tsk->cg_list))
+ list_move(&tsk->cg_list, &newcg->tasks);
+ write_unlock(&css_set_lock);
+
+ /*
+ * We just gained a reference on oldcg by taking it from the task. As
+ * trading it for newcg is protected by cgroup_mutex, we're safe to drop
+ * it here; it will be freed under RCU.
+ */
+ put_css_set(oldcg);
+
+ set_bit(CGRP_RELEASABLE, &oldcgrp->flags);
+ return 0;
+}
+
/**
* cgroup_attach_task - attach task 'tsk' to cgroup 'cgrp'
* @cgrp: the cgroup the task is attaching to
*/
int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
{
- int retval = 0;
+ int retval;
struct cgroup_subsys *ss, *failed_ss = NULL;
struct cgroup *oldcgrp;
- struct css_set *cg;
- struct css_set *newcg;
struct cgroupfs_root *root = cgrp->root;
/* Nothing to do if the task is already in that cgroup */
for_each_subsys(root, ss) {
if (ss->can_attach) {
- retval = ss->can_attach(ss, cgrp, tsk, false);
+ retval = ss->can_attach(ss, cgrp, tsk);
if (retval) {
/*
* Remember on which subsystem the can_attach()
goto out;
}
}
+ if (ss->can_attach_task) {
+ retval = ss->can_attach_task(cgrp, tsk);
+ if (retval) {
+ failed_ss = ss;
+ goto out;
+ }
+ }
}
- task_lock(tsk);
- cg = tsk->cgroups;
- get_css_set(cg);
- task_unlock(tsk);
- /*
- * Locate or allocate a new css_set for this task,
- * based on its final set of cgroups
- */
- newcg = find_css_set(cg, cgrp);
- put_css_set(cg);
- if (!newcg) {
- retval = -ENOMEM;
- goto out;
- }
-
- task_lock(tsk);
- if (tsk->flags & PF_EXITING) {
- task_unlock(tsk);
- put_css_set(newcg);
- retval = -ESRCH;
+ retval = cgroup_task_migrate(cgrp, oldcgrp, tsk, false);
+ if (retval)
goto out;
- }
- rcu_assign_pointer(tsk->cgroups, newcg);
- task_unlock(tsk);
-
- /* Update the css_set linked lists if we're using them */
- write_lock(&css_set_lock);
- if (!list_empty(&tsk->cg_list)) {
- list_del(&tsk->cg_list);
- list_add(&tsk->cg_list, &newcg->tasks);
- }
- write_unlock(&css_set_lock);
for_each_subsys(root, ss) {
+ if (ss->pre_attach)
+ ss->pre_attach(cgrp);
+ if (ss->attach_task)
+ ss->attach_task(cgrp, tsk);
if (ss->attach)
- ss->attach(ss, cgrp, oldcgrp, tsk, false);
+ ss->attach(ss, cgrp, oldcgrp, tsk);
}
- set_bit(CGRP_RELEASABLE, &oldcgrp->flags);
+
synchronize_rcu();
- put_css_set(cg);
/*
* wake up rmdir() waiter. the rmdir should fail since the cgroup
*/
break;
if (ss->cancel_attach)
- ss->cancel_attach(ss, cgrp, tsk, false);
+ ss->cancel_attach(ss, cgrp, tsk);
+ }
+ }
+ 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);
+
+/*
+ * cgroup_attach_proc works in two stages, the first of which prefetches all
+ * new css_sets needed (to make sure we have enough memory before committing
+ * to the move) and stores them in a list of entries of the following type.
+ * TODO: possible optimization: use css_set->rcu_head for chaining instead
+ */
+struct cg_list_entry {
+ struct css_set *cg;
+ struct list_head links;
+};
+
+static bool css_set_check_fetched(struct cgroup *cgrp,
+ struct task_struct *tsk, struct css_set *cg,
+ struct list_head *newcg_list)
+{
+ struct css_set *newcg;
+ struct cg_list_entry *cg_entry;
+ struct cgroup_subsys_state *template[CGROUP_SUBSYS_COUNT];
+
+ read_lock(&css_set_lock);
+ newcg = find_existing_css_set(cg, cgrp, template);
+ if (newcg)
+ get_css_set(newcg);
+ read_unlock(&css_set_lock);
+
+ /* doesn't exist at all? */
+ if (!newcg)
+ return false;
+ /* see if it's already in the list */
+ list_for_each_entry(cg_entry, newcg_list, links) {
+ if (cg_entry->cg == newcg) {
+ put_css_set(newcg);
+ return true;
+ }
+ }
+
+ /* not found */
+ put_css_set(newcg);
+ return false;
+}
+
+/*
+ * Find the new css_set and store it in the list in preparation for moving the
+ * given task to the given cgroup. Returns 0 or -ENOMEM.
+ */
+static int css_set_prefetch(struct cgroup *cgrp, struct css_set *cg,
+ struct list_head *newcg_list)
+{
+ struct css_set *newcg;
+ struct cg_list_entry *cg_entry;
+
+ /* ensure a new css_set will exist for this thread */
+ newcg = find_css_set(cg, cgrp);
+ if (!newcg)
+ return -ENOMEM;
+ /* add it to the list */
+ cg_entry = kmalloc(sizeof(struct cg_list_entry), GFP_KERNEL);
+ if (!cg_entry) {
+ put_css_set(newcg);
+ return -ENOMEM;
+ }
+ cg_entry->cg = newcg;
+ list_add(&cg_entry->links, newcg_list);
+ return 0;
+}
+
+/**
+ * cgroup_attach_proc - attach all threads in a threadgroup to a cgroup
+ * @cgrp: the cgroup to attach to
+ * @leader: the threadgroup leader task_struct of the group to be attached
+ *
+ * Call holding cgroup_mutex and the threadgroup_fork_lock of the leader. Will
+ * take task_lock of each thread in leader's threadgroup individually in turn.
+ */
+int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
+{
+ int retval, i, group_size;
+ struct cgroup_subsys *ss, *failed_ss = NULL;
+ bool cancel_failed_ss = false;
+ /* guaranteed to be initialized later, but the compiler needs this */
+ struct cgroup *oldcgrp = NULL;
+ struct css_set *oldcg;
+ struct cgroupfs_root *root = cgrp->root;
+ /* threadgroup list cursor and array */
+ struct task_struct *tsk;
+ struct flex_array *group;
+ /*
+ * we need to make sure we have css_sets for all the tasks we're
+ * going to move -before- we actually start moving them, so that in
+ * case we get an ENOMEM we can bail out before making any changes.
+ */
+ struct list_head newcg_list;
+ struct cg_list_entry *cg_entry, *temp_nobe;
+
+ /*
+ * step 0: in order to do expensive, possibly blocking operations for
+ * every thread, we cannot iterate the thread group list, since it needs
+ * rcu or tasklist locked. instead, build an array of all threads in the
+ * group - threadgroup_fork_lock prevents new threads from appearing,
+ * and if threads exit, this will just be an over-estimate.
+ */
+ group_size = get_nr_threads(leader);
+ /* flex_array supports very large thread-groups better than kmalloc. */
+ group = flex_array_alloc(sizeof(struct task_struct *), group_size,
+ GFP_KERNEL);
+ if (!group)
+ return -ENOMEM;
+ /* pre-allocate to guarantee space while iterating in rcu read-side. */
+ retval = flex_array_prealloc(group, 0, group_size - 1, GFP_KERNEL);
+ if (retval)
+ goto out_free_group_list;
+
+ /* prevent changes to the threadgroup list while we take a snapshot. */
+ rcu_read_lock();
+ if (!thread_group_leader(leader)) {
+ /*
+ * a race with de_thread from another thread's exec() may strip
+ * us of our leadership, making while_each_thread unsafe to use
+ * on this task. if this happens, there is no choice but to
+ * throw this task away and try again (from cgroup_procs_write);
+ * this is "double-double-toil-and-trouble-check locking".
+ */
+ rcu_read_unlock();
+ retval = -EAGAIN;
+ goto out_free_group_list;
+ }
+ /* take a reference on each task in the group to go in the array. */
+ tsk = leader;
+ i = 0;
+ do {
+ /* as per above, nr_threads may decrease, but not increase. */
+ BUG_ON(i >= group_size);
+ get_task_struct(tsk);
+ /*
+ * saying GFP_ATOMIC has no effect here because we did prealloc
+ * earlier, but it's good form to communicate our expectations.
+ */
+ retval = flex_array_put_ptr(group, i, tsk, GFP_ATOMIC);
+ BUG_ON(retval != 0);
+ i++;
+ } while_each_thread(leader, tsk);
+ /* remember the number of threads in the array for later. */
+ group_size = i;
+ rcu_read_unlock();
+
+ /*
+ * step 1: check that we can legitimately attach to the cgroup.
+ */
+ for_each_subsys(root, ss) {
+ if (ss->can_attach) {
+ retval = ss->can_attach(ss, cgrp, leader);
+ if (retval) {
+ failed_ss = ss;
+ goto out_cancel_attach;
+ }
+ }
+ /* a callback to be run on every thread in the threadgroup. */
+ if (ss->can_attach_task) {
+ /* run on each task in the threadgroup. */
+ for (i = 0; i < group_size; i++) {
+ tsk = flex_array_get_ptr(group, i);
+ retval = ss->can_attach_task(cgrp, tsk);
+ if (retval) {
+ failed_ss = ss;
+ cancel_failed_ss = true;
+ goto out_cancel_attach;
+ }
+ }
+ }
+ }
+
+ /*
+ * step 2: make sure css_sets exist for all threads to be migrated.
+ * we use find_css_set, which allocates a new one if necessary.
+ */
+ INIT_LIST_HEAD(&newcg_list);
+ for (i = 0; i < group_size; i++) {
+ tsk = flex_array_get_ptr(group, i);
+ /* nothing to do if this task is already in the cgroup */
+ oldcgrp = task_cgroup_from_root(tsk, root);
+ if (cgrp == oldcgrp)
+ continue;
+ /* get old css_set pointer */
+ task_lock(tsk);
+ oldcg = tsk->cgroups;
+ get_css_set(oldcg);
+ task_unlock(tsk);
+ /* see if the new one for us is already in the list? */
+ if (css_set_check_fetched(cgrp, tsk, oldcg, &newcg_list)) {
+ /* was already there, nothing to do. */
+ put_css_set(oldcg);
+ } else {
+ /* we don't already have it. get new one. */
+ retval = css_set_prefetch(cgrp, oldcg, &newcg_list);
+ put_css_set(oldcg);
+ if (retval)
+ goto out_list_teardown;
+ }
+ }
+
+ /*
+ * step 3: now that we're guaranteed success wrt the css_sets, proceed
+ * to move all tasks to the new cgroup, calling ss->attach_task for each
+ * one along the way. there are no failure cases after here, so this is
+ * the commit point.
+ */
+ for_each_subsys(root, ss) {
+ if (ss->pre_attach)
+ ss->pre_attach(cgrp);
+ }
+ for (i = 0; i < group_size; i++) {
+ tsk = flex_array_get_ptr(group, i);
+ /* leave current thread as it is if it's already there */
+ oldcgrp = task_cgroup_from_root(tsk, root);
+ if (cgrp == oldcgrp)
+ continue;
+ /* attach each task to each subsystem */
+ for_each_subsys(root, ss) {
+ if (ss->attach_task)
+ ss->attach_task(cgrp, tsk);
+ }
+ /* if the thread is PF_EXITING, it can just get skipped. */
+ retval = cgroup_task_migrate(cgrp, oldcgrp, tsk, true);
+ BUG_ON(retval != 0 && retval != -ESRCH);
+ }
+ /* nothing is sensitive to fork() after this point. */
+
+ /*
+ * step 4: do expensive, non-thread-specific subsystem callbacks.
+ * TODO: if ever a subsystem needs to know the oldcgrp for each task
+ * being moved, this call will need to be reworked to communicate that.
+ */
+ for_each_subsys(root, ss) {
+ if (ss->attach)
+ ss->attach(ss, cgrp, oldcgrp, leader);
+ }
+
+ /*
+ * step 5: success! and cleanup
+ */
+ synchronize_rcu();
+ cgroup_wakeup_rmdir_waiter(cgrp);
+ retval = 0;
+out_list_teardown:
+ /* clean up the list of prefetched css_sets. */
+ list_for_each_entry_safe(cg_entry, temp_nobe, &newcg_list, links) {
+ list_del(&cg_entry->links);
+ put_css_set(cg_entry->cg);
+ kfree(cg_entry);
+ }
+out_cancel_attach:
+ /* same deal as in cgroup_attach_task */
+ if (retval) {
+ for_each_subsys(root, ss) {
+ if (ss == failed_ss) {
+ if (cancel_failed_ss && ss->cancel_attach)
+ ss->cancel_attach(ss, cgrp, leader);
+ break;
+ }
+ if (ss->cancel_attach)
+ ss->cancel_attach(ss, cgrp, leader);
}
}
+ /* clean up the array of referenced threads in the group. */
+ for (i = 0; i < group_size; i++) {
+ tsk = flex_array_get_ptr(group, i);
+ put_task_struct(tsk);
+ }
+out_free_group_list:
+ flex_array_free(group);
return retval;
}
/*
- * Attach task with pid 'pid' to cgroup 'cgrp'. Call with cgroup_mutex
- * held. May take task_lock of task
+ * Find the task_struct of the task to attach by vpid and pass it along to the
+ * function to attach either it or all tasks in its threadgroup. Will take
+ * cgroup_mutex; may take task_lock of task.
*/
-static int attach_task_by_pid(struct cgroup *cgrp, u64 pid)
+static int attach_task_by_pid(struct cgroup *cgrp, u64 pid, bool threadgroup)
{
struct task_struct *tsk;
const struct cred *cred = current_cred(), *tcred;
int ret;
+ if (!cgroup_lock_live_group(cgrp))
+ return -ENODEV;
+
if (pid) {
rcu_read_lock();
tsk = find_task_by_vpid(pid);
- if (!tsk || tsk->flags & PF_EXITING) {
+ if (!tsk) {
+ rcu_read_unlock();
+ cgroup_unlock();
+ return -ESRCH;
+ }
+ if (threadgroup) {
+ /*
+ * RCU protects this access, since tsk was found in the
+ * tid map. a race with de_thread may cause group_leader
+ * to stop being the leader, but cgroup_attach_proc will
+ * detect it later.
+ */
+ tsk = tsk->group_leader;
+ } else if (tsk->flags & PF_EXITING) {
+ /* optimization for the single-task-only case */
rcu_read_unlock();
+ cgroup_unlock();
return -ESRCH;
}
+ /*
+ * even if we're attaching all tasks in the thread group, we
+ * only need to check permissions on one of them.
+ */
tcred = __task_cred(tsk);
if (cred->euid &&
cred->euid != tcred->uid &&
cred->euid != tcred->suid) {
rcu_read_unlock();
+ cgroup_unlock();
return -EACCES;
}
get_task_struct(tsk);
rcu_read_unlock();
} else {
- tsk = current;
+ if (threadgroup)
+ tsk = current->group_leader;
+ else
+ tsk = current;
get_task_struct(tsk);
}
- ret = cgroup_attach_task(cgrp, tsk);
+ if (threadgroup) {
+ threadgroup_fork_write_lock(tsk);
+ ret = cgroup_attach_proc(cgrp, tsk);
+ threadgroup_fork_write_unlock(tsk);
+ } else {
+ ret = cgroup_attach_task(cgrp, tsk);
+ }
put_task_struct(tsk);
+ cgroup_unlock();
return ret;
}
static int cgroup_tasks_write(struct cgroup *cgrp, struct cftype *cft, u64 pid)
+{
+ return attach_task_by_pid(cgrp, pid, false);
+}
+
+static int cgroup_procs_write(struct cgroup *cgrp, struct cftype *cft, u64 tgid)
{
int ret;
- if (!cgroup_lock_live_group(cgrp))
- return -ENODEV;
- ret = attach_task_by_pid(cgrp, pid);
- cgroup_unlock();
+ do {
+ /*
+ * attach_proc fails with -EAGAIN if threadgroup leadership
+ * changes in the middle of the operation, in which case we need
+ * to find the task_struct for the new leader and start over.
+ */
+ ret = attach_task_by_pid(cgrp, tgid, true);
+ } while (ret == -EAGAIN);
return ret;
}
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);
};
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
*/
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)
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;
remove);
struct cgroup *cgrp = event->cgrp;
- /* TODO: check return code */
event->cft->unregister_event(cgrp, event->cft, event->eventfd);
eventfd_ctx_put(event->eventfd);
- remove_wait_queue(event->wqh, &event->wait);
kfree(event);
+ dput(cgrp->dentry);
}
/*
unsigned long flags = (unsigned long)key;
if (flags & POLLHUP) {
+ __remove_wait_queue(event->wqh, &event->wait);
spin_lock(&cgrp->event_list_lock);
list_del(&event->list);
spin_unlock(&cgrp->event_list_lock);
}
/* the process need read permission on control file */
- ret = file_permission(cfile, MAY_READ);
+ /* AV: shouldn't we check that it's been opened for read instead? */
+ ret = inode_permission(cfile->f_path.dentry->d_inode, MAY_READ);
if (ret < 0)
goto fail;
goto fail;
}
+ /*
+ * Events should be removed after rmdir of cgroup directory, but before
+ * destroying subsystem state objects. Let's take reference to cgroup
+ * directory dentry to do that.
+ */
+ dget(cgrp->dentry);
+
spin_lock(&cgrp->event_list_lock);
list_add(&event->list, &cgrp->event_list);
spin_unlock(&cgrp->event_list_lock);
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
*/
{
.name = CGROUP_FILE_GENERIC_PREFIX "procs",
.open = cgroup_procs_open,
- /* .write_u64 = cgroup_procs_write, TODO */
+ .write_u64 = cgroup_procs_write,
.release = cgroup_pidlist_release,
- .mode = S_IRUGO,
+ .mode = S_IRUGO | S_IWUSR,
},
{
.name = "notify_on_release",
.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 = {
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);
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);
struct dentry *d;
struct cgroup *parent;
DEFINE_WAIT(wait);
+ struct cgroup_event *event, *tmp;
int ret;
/* the vfs holds both inode->i_mutex already */
spin_lock(&release_list_lock);
set_bit(CGRP_REMOVED, &cgrp->flags);
if (!list_empty(&cgrp->release_list))
- list_del(&cgrp->release_list);
+ list_del_init(&cgrp->release_list);
spin_unlock(&release_list_lock);
cgroup_lock_hierarchy(cgrp->root);
/* delete this cgroup from parent->children */
- list_del(&cgrp->sibling);
+ list_del_init(&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);
set_bit(CGRP_RELEASABLE, &parent->flags);
check_for_release(parent);
+ /*
+ * Unregister events and notify userspace.
+ * Notify userspace about cgroup removing only after rmdir of cgroup
+ * directory to avoid race between userspace and kernelspace
+ */
+ spin_lock(&cgrp->event_list_lock);
+ list_for_each_entry_safe(event, tmp, &cgrp->event_list, list) {
+ list_del(&event->list);
+ remove_wait_queue(event->wqh, &event->wait);
+ eventfd_signal(event->eventfd, 1);
+ schedule_work(&event->remove);
+ }
+ spin_unlock(&cgrp->event_list_lock);
+
mutex_unlock(&cgroup_mutex);
return 0;
}
* @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.
*/
subsys[ss->subsys_id] = NULL;
/* remove subsystem from rootnode's list of subsystems */
- list_del(&ss->sibling);
+ list_del_init(&ss->sibling);
/*
* disentangle the css from all css_sets attached to the dummytop. as
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);
*/
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.
if (!list_empty(&tsk->cg_list)) {
write_lock(&css_set_lock);
if (!list_empty(&tsk->cg_list))
- list_del(&tsk->cg_list);
+ list_del_init(&tsk->cg_list);
write_unlock(&css_set_lock);
}
task_lock(tsk);
cg = tsk->cgroups;
tsk->cgroups = &init_css_set;
- task_unlock(tsk);
- if (cg)
- put_css_set_taskexit(cg);
-}
-
-/**
- * cgroup_clone - clone the cgroup the given subsystem is attached to
- * @tsk: the task to be moved
- * @subsys: the given subsystem
- * @nodename: the name for the new cgroup
- *
- * Duplicate the current cgroup in the hierarchy that the given
- * subsystem is attached to, and move this task into the new
- * child.
- */
-int cgroup_clone(struct task_struct *tsk, struct cgroup_subsys *subsys,
- char *nodename)
-{
- struct dentry *dentry;
- int ret = 0;
- struct cgroup *parent, *child;
- struct inode *inode;
- struct css_set *cg;
- struct cgroupfs_root *root;
- struct cgroup_subsys *ss;
-
- /* We shouldn't be called by an unregistered subsystem */
- BUG_ON(!subsys->active);
-
- /* First figure out what hierarchy and cgroup we're dealing
- * with, and pin them so we can drop cgroup_mutex */
- mutex_lock(&cgroup_mutex);
- again:
- root = subsys->root;
- if (root == &rootnode) {
- mutex_unlock(&cgroup_mutex);
- return 0;
- }
- /* Pin the hierarchy */
- if (!atomic_inc_not_zero(&root->sb->s_active)) {
- /* We race with the final deactivate_super() */
- mutex_unlock(&cgroup_mutex);
- return 0;
+ 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);
+ }
+ }
}
-
- /* Keep the cgroup alive */
- task_lock(tsk);
- parent = task_cgroup(tsk, subsys->subsys_id);
- cg = tsk->cgroups;
- get_css_set(cg);
task_unlock(tsk);
- mutex_unlock(&cgroup_mutex);
-
- /* Now do the VFS work to create a cgroup */
- inode = parent->dentry->d_inode;
-
- /* Hold the parent directory mutex across this operation to
- * stop anyone else deleting the new cgroup */
- mutex_lock(&inode->i_mutex);
- dentry = lookup_one_len(nodename, parent->dentry, strlen(nodename));
- if (IS_ERR(dentry)) {
- printk(KERN_INFO
- "cgroup: Couldn't allocate dentry for %s: %ld\n", nodename,
- PTR_ERR(dentry));
- ret = PTR_ERR(dentry);
- goto out_release;
- }
-
- /* Create the cgroup directory, which also creates the cgroup */
- ret = vfs_mkdir(inode, dentry, 0755);
- child = __d_cgrp(dentry);
- dput(dentry);
- if (ret) {
- printk(KERN_INFO
- "Failed to create cgroup %s: %d\n", nodename,
- ret);
- goto out_release;
- }
-
- /* The cgroup now exists. Retake cgroup_mutex and check
- * that we're still in the same state that we thought we
- * were. */
- mutex_lock(&cgroup_mutex);
- if ((root != subsys->root) ||
- (parent != task_cgroup(tsk, subsys->subsys_id))) {
- /* Aargh, we raced ... */
- mutex_unlock(&inode->i_mutex);
- put_css_set(cg);
-
- deactivate_super(root->sb);
- /* The cgroup is still accessible in the VFS, but
- * we're not going to try to rmdir() it at this
- * point. */
- printk(KERN_INFO
- "Race in cgroup_clone() - leaking cgroup %s\n",
- nodename);
- goto again;
- }
-
- /* do any required auto-setup */
- for_each_subsys(root, ss) {
- if (ss->post_clone)
- ss->post_clone(ss, child);
- }
-
- /* All seems fine. Finish by moving the task into the new cgroup */
- ret = cgroup_attach_task(child, tsk);
- mutex_unlock(&cgroup_mutex);
-
- out_release:
- mutex_unlock(&inode->i_mutex);
-
- mutex_lock(&cgroup_mutex);
- put_css_set(cg);
- mutex_unlock(&cgroup_mutex);
- deactivate_super(root->sb);
- return ret;
+ if (cg)
+ put_css_set_taskexit(cg);
}
/**
*/
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, atomic_read(&css->refcnt));
if (cssid)
return cssid->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, atomic_read(&css->refcnt));
if (cssid)
return cssid->depth;
}
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);
-
- if (!child_id || !root_id || (child_id->depth < root_id->depth))
- return false;
- return child_id->stack[root_id->depth] == root_id->id;
-}
+ struct css_id *child_id;
+ struct css_id *root_id;
+ bool ret = true;
-static void __free_css_id_cb(struct rcu_head *head)
-{
- struct css_id *id;
-
- id = container_of(head, struct css_id, rcu_head);
- kfree(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;
}
void free_css_id(struct cgroup_subsys *ss, struct cgroup_subsys_state *css)
spin_lock(&ss->id_lock);
idr_remove(&ss->idr, id->id);
spin_unlock(&ss->id_lock);
- call_rcu(&id->rcu_head, __free_css_id_cb);
+ kfree_rcu(id, rcu_head);
}
EXPORT_SYMBOL_GPL(free_css_id);
{
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))
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)