Merge branch 'for-4.7-fixes' of git://git.kernel.org/pub/scm/linux/ke…

…rnel/git/tj/cgroup

Pull more cgroup updates from Tejun Heo:
 "I forgot to include the patches which got applied to for-4.7-fixes
  late during last cycle.

  Eric's three patches fix bugs introduced with the namespace support"

* 'for-4.7-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup:
  cgroupns: Only allow creation of hierarchies in the initial cgroup namespace
  cgroupns: Close race between cgroup_post_fork and copy_cgroup_ns
  cgroupns: Fix the locking in copy_cgroup_ns

kernel/cgroup.c

@@ -2209,12 +2209,8 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type,
 		goto out_unlock;
 	}
 
-	/*
-	 * We know this subsystem has not yet been bound.  Users in a non-init
-	 * user namespace may only mount hierarchies with no bound subsystems,
-	 * i.e. 'none,name=user1'
-	 */
-	if (!opts.none && !capable(CAP_SYS_ADMIN)) {
+	/* Hierarchies may only be created in the initial cgroup namespace. */
+	if (ns != &init_cgroup_ns) {
 		ret = -EPERM;
 		goto out_unlock;
 	}
@@ -2956,6 +2952,7 @@ int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk)
 	int retval = 0;
 
 	mutex_lock(&cgroup_mutex);
+	percpu_down_write(&cgroup_threadgroup_rwsem);
 	for_each_root(root) {
 		struct cgroup *from_cgrp;
 
@@ -2970,6 +2967,7 @@ int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk)
 		if (retval)
 			break;
 	}
+	percpu_up_write(&cgroup_threadgroup_rwsem);
 	mutex_unlock(&cgroup_mutex);
 
 	return retval;
@@ -4337,6 +4335,8 @@ int cgroup_transfer_tasks(struct cgroup *to, struct cgroup *from)
 
 	mutex_lock(&cgroup_mutex);
 
+	percpu_down_write(&cgroup_threadgroup_rwsem);
+
 	/* all tasks in @from are being moved, all csets are source */
 	spin_lock_irq(&css_set_lock);
 	list_for_each_entry(link, &from->cset_links, cset_link)
@@ -4365,6 +4365,7 @@ int cgroup_transfer_tasks(struct cgroup *to, struct cgroup *from)
 	} while (task && !ret);
 out_err:
 	cgroup_migrate_finish(&preloaded_csets);
+	percpu_up_write(&cgroup_threadgroup_rwsem);
 	mutex_unlock(&cgroup_mutex);
 	return ret;
 }
@@ -6339,14 +6340,11 @@ struct cgroup_namespace *copy_cgroup_ns(unsigned long flags,
 	if (!ns_capable(user_ns, CAP_SYS_ADMIN))
 		return ERR_PTR(-EPERM);
 
-	mutex_lock(&cgroup_mutex);
+	/* It is not safe to take cgroup_mutex here */
 	spin_lock_irq(&css_set_lock);
-
 	cset = task_css_set(current);
 	get_css_set(cset);
-
 	spin_unlock_irq(&css_set_lock);
-	mutex_unlock(&cgroup_mutex);
 
 	new_ns = alloc_cgroup_ns();
 	if (IS_ERR(new_ns)) {