cgroup: remove the ns_cgroup

The ns_cgroup is an annoying cgroup at the namespace / cgroup frontier and
leads to some problems:

  * cgroup creation is out-of-control
  * cgroup name can conflict when pids are looping
  * it is not possible to have a single process handling a lot of
    namespaces without falling in a exponential creation time
  * we may want to create a namespace without creating a cgroup

  The ns_cgroup was replaced by a compatibility flag 'clone_children',
  where a newly created cgroup will copy the parent cgroup values.
  The userspace has to manually create a cgroup and add a task to
  the 'tasks' file.

This patch removes the ns_cgroup as suggested in the following thread:

https://lists.linux-foundation.org/pipermail/containers/2009-June/018616.html

The 'cgroup_clone' function is removed because it is no longer used.

This is a userspace-visible change.  Commit 45531757b45c ("cgroup: notify
ns_cgroup deprecated") (merged into 2.6.27) caused the kernel to emit a
printk warning users that the feature is planned for removal.  Since that
time we have heard from XXX users who were affected by this.

Signed-off-by: Daniel Lezcano <daniel.lezcano@free.fr>
Signed-off-by: Serge E. Hallyn <serge.hallyn@canonical.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Jamal Hadi Salim <hadi@cyberus.ca>
Reviewed-by: Li Zefan <lizf@cn.fujitsu.com>
Acked-by: Paul Menage <menage@google.com>
Acked-by: Matt Helsley <matthltc@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 0 insertions, 116 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 00a884342d3d..2731d115d725 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -4630,122 +4630,6 @@ void cgroup_exit(struct task_struct *tsk, int run_callbacks)
 }
 
 /**
- * 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;
-        }
-
-        /* 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;
-}
-
-/**
  * cgroup_is_descendant - see if @cgrp is a descendant of @task's cgrp
  * @cgrp: the cgroup in question
  * @task: the task in question