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>

6 files changed, 3 insertions, 249 deletions

diff --git a/kernel/Makefile b/kernel/Makefile
index e9cf19155b46..2d64cfcc8b42 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -61,7 +61,6 @@ obj-$(CONFIG_COMPAT) += compat.o
 obj-$(CONFIG_CGROUPS) += cgroup.o
 obj-$(CONFIG_CGROUP_FREEZER) += cgroup_freezer.o
 obj-$(CONFIG_CPUSETS) += cpuset.o
-obj-$(CONFIG_CGROUP_NS) += ns_cgroup.o
 obj-$(CONFIG_UTS_NS) += utsname.o
 obj-$(CONFIG_USER_NS) += user_namespace.o
 obj-$(CONFIG_PID_NS) += pid_namespace.o
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
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 55b297d78adc..1ceeb049c827 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -1802,10 +1802,9 @@ static int cpuset_populate(struct cgroup_subsys *ss, struct cgroup *cont)
 }
 
 /*
- * post_clone() is called at the end of cgroup_clone().
- * 'cgroup' was just created automatically as a result of
- * a cgroup_clone(), and the current task is about to
- * be moved into 'cgroup'.
+ * post_clone() is called during cgroup_create() when the
+ * clone_children mount argument was specified.  The cgroup
+ * can not yet have any tasks.
  *
  * Currently we refuse to set up the cgroup - thereby
  * refusing the task to be entered, and as a result refusing
diff --git a/kernel/fork.c b/kernel/fork.c
index 1fa9d940e301..1f84099ecce6 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1229,12 +1229,6 @@ static struct task_struct *copy_process(unsigned long clone_flags,
         if (clone_flags & CLONE_THREAD)
                 p->tgid = current->tgid;
 
-        if (current->nsproxy != p->nsproxy) {
-                retval = ns_cgroup_clone(p, pid);
-                if (retval)
-                        goto bad_fork_free_pid;
-        }
-
         p->set_child_tid = (clone_flags & CLONE_CHILD_SETTID) ? child_tidptr : NULL;
         /*
          * Clear TID on mm_release()?
diff --git a/kernel/ns_cgroup.c b/kernel/ns_cgroup.c
deleted file mode 100644
index 2c98ad94ba0e..000000000000
--- a/kernel/ns_cgroup.c
+++ /dev/null
@@ -1,118 +0,0 @@
-/*
- * ns_cgroup.c - namespace cgroup subsystem
- *
- * Copyright 2006, 2007 IBM Corp
- */
-
-#include <linux/module.h>
-#include <linux/cgroup.h>
-#include <linux/fs.h>
-#include <linux/proc_fs.h>
-#include <linux/slab.h>
-#include <linux/nsproxy.h>
-
-struct ns_cgroup {
-        struct cgroup_subsys_state css;
-};
-
-struct cgroup_subsys ns_subsys;
-
-static inline struct ns_cgroup *cgroup_to_ns(
-                struct cgroup *cgroup)
-{
-        return container_of(cgroup_subsys_state(cgroup, ns_subsys_id),
-                            struct ns_cgroup, css);
-}
-
-int ns_cgroup_clone(struct task_struct *task, struct pid *pid)
-{
-        char name[PROC_NUMBUF];
-
-        snprintf(name, PROC_NUMBUF, "%d", pid_vnr(pid));
-        return cgroup_clone(task, &ns_subsys, name);
-}
-
-/*
- * Rules:
- *   1. you can only enter a cgroup which is a descendant of your current
- *     cgroup
- *   2. you can only place another process into a cgroup if
- *     a. you have CAP_SYS_ADMIN
- *     b. your cgroup is an ancestor of task's destination cgroup
- *       (hence either you are in the same cgroup as task, or in an
- *        ancestor cgroup thereof)
- */
-static int ns_can_attach(struct cgroup_subsys *ss, struct cgroup *new_cgroup,
-                         struct task_struct *task, bool threadgroup)
-{
-        if (current != task) {
-                if (!capable(CAP_SYS_ADMIN))
-                        return -EPERM;
-
-                if (!cgroup_is_descendant(new_cgroup, current))
-                        return -EPERM;
-        }
-
-        if (!cgroup_is_descendant(new_cgroup, task))
-                return -EPERM;
-
-        if (threadgroup) {
-                struct task_struct *c;
-                rcu_read_lock();
-                list_for_each_entry_rcu(c, &task->thread_group, thread_group) {
-                        if (!cgroup_is_descendant(new_cgroup, c)) {
-                                rcu_read_unlock();
-                                return -EPERM;
-                        }
-                }
-                rcu_read_unlock();
-        }
-
-        return 0;
-}
-
-/*
- * Rules: you can only create a cgroup if
- *     1. you are capable(CAP_SYS_ADMIN)
- *     2. the target cgroup is a descendant of your own cgroup
- */
-static struct cgroup_subsys_state *ns_create(struct cgroup_subsys *ss,
-                                                struct cgroup *cgroup)
-{
-        struct ns_cgroup *ns_cgroup;
-
-        if (!capable(CAP_SYS_ADMIN))
-                return ERR_PTR(-EPERM);
-        if (!cgroup_is_descendant(cgroup, current))
-                return ERR_PTR(-EPERM);
-        if (test_bit(CGRP_CLONE_CHILDREN, &cgroup->flags)) {
-                printk("ns_cgroup can't be created with parent "
-                       "'clone_children' set.\n");
-                return ERR_PTR(-EINVAL);
-        }
-
-        printk_once("ns_cgroup deprecated: consider using the "
-                    "'clone_children' flag without the ns_cgroup.\n");
-
-        ns_cgroup = kzalloc(sizeof(*ns_cgroup), GFP_KERNEL);
-        if (!ns_cgroup)
-                return ERR_PTR(-ENOMEM);
-        return &ns_cgroup->css;
-}
-
-static void ns_destroy(struct cgroup_subsys *ss,
-                        struct cgroup *cgroup)
-{
-        struct ns_cgroup *ns_cgroup;
-
-        ns_cgroup = cgroup_to_ns(cgroup);
-        kfree(ns_cgroup);
-}
-
-struct cgroup_subsys ns_subsys = {
-        .name = "ns",
-        .can_attach = ns_can_attach,
-        .create = ns_create,
-        .destroy  = ns_destroy,
-        .subsys_id = ns_subsys_id,
-};
diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c
index 5424e37673ed..d6a00f3de15d 100644
--- a/kernel/nsproxy.c
+++ b/kernel/nsproxy.c
@@ -201,10 +201,6 @@ int unshare_nsproxy_namespaces(unsigned long unshare_flags,
                 goto out;
         }
 
-        err = ns_cgroup_clone(current, task_pid(current));
-        if (err)
-                put_nsproxy(*new_nsp);
-
 out:
         return err;
 }