cgroups: implement namespace tracking subsystem

When a task enters a new namespace via a clone() or unshare(), a new cgroup
is created and the task moves into it.

This version names cgroups which are automatically created using
cgroup_clone() as "node_<pid>" where pid is the pid of the unsharing or
cloned process.  (Thanks Pavel for the idea) This is safe because if the
process unshares again, it will create

	/cgroups/(...)/node_<pid>/node_<pid>

The only possibilities (AFAICT) for a -EEXIST on unshare are

	1. pid wraparound
	2. a process fails an unshare, then tries again.

Case 1 is unlikely enough that I ignore it (at least for now).  In case 2, the
node_<pid> will be empty and can be rmdir'ed to make the subsequent unshare()
succeed.

Changelog:
	Name cloned cgroups as "node_<pid>".

[clg@fr.ibm.com: fix order of cgroup subsystems in init/Kconfig]
Signed-off-by: Serge E. Hallyn <serue@us.ibm.com>
Cc: Paul Menage <menage@google.com>
Signed-off-by: Cedric Le Goater <clg@fr.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 16 insertions, 1 deletions

diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c
index 049e7c0ac566..ac99837e7a04 100644
--- a/kernel/nsproxy.c
+++ b/kernel/nsproxy.c
@@ -156,7 +156,14 @@ int copy_namespaces(unsigned long flags, struct task_struct *tsk)
                 goto out;
         }
 
+        err = ns_cgroup_clone(tsk);
+        if (err) {
+                put_nsproxy(new_ns);
+                goto out;
+        }
+
         tsk->nsproxy = new_ns;
+
 out:
         put_nsproxy(old_ns);
         return err;
@@ -196,8 +203,16 @@ int unshare_nsproxy_namespaces(unsigned long unshare_flags,
 
         *new_nsp = create_new_namespaces(unshare_flags, current,
                                 new_fs ? new_fs : current->fs);
-        if (IS_ERR(*new_nsp))
+        if (IS_ERR(*new_nsp)) {
                 err = PTR_ERR(*new_nsp);
+                goto out;
+        }
+
+        err = ns_cgroup_clone(current);
+        if (err)
+                put_nsproxy(*new_nsp);
+
+out:
         return err;
 }