--- zzzz-none-000/linux-3.10.107/kernel/pid_namespace.c	2017-06-27 09:49:32.000000000 +0000
+++ scorpion-7490-727/linux-3.10.107/kernel/pid_namespace.c	2021-02-04 17:41:59.000000000 +0000
@@ -105,9 +105,10 @@
 	if (ns->pid_cachep == NULL)
 		goto out_free_map;
 
-	err = proc_alloc_inum(&ns->proc_inum);
+	err = ns_alloc_inum(&ns->ns);
 	if (err)
 		goto out_free_map;
+	ns->ns.ops = &pidns_operations;
 
 	kref_init(&ns->kref);
 	ns->level = level;
@@ -132,15 +133,21 @@
 	return ERR_PTR(err);
 }
 
+static void delayed_free_pidns(struct rcu_head *p)
+{
+	kmem_cache_free(pid_ns_cachep,
+			container_of(p, struct pid_namespace, rcu));
+}
+
 static void destroy_pid_namespace(struct pid_namespace *ns)
 {
 	int i;
 
-	proc_free_inum(ns->proc_inum);
+	ns_free_inum(&ns->ns);
 	for (i = 0; i < PIDMAP_ENTRIES; i++)
 		kfree(ns->pidmap[i].page);
 	put_user_ns(ns->user_ns);
-	kmem_cache_free(pid_ns_cachep, ns);
+	call_rcu(&ns->rcu, delayed_free_pidns);
 }
 
 struct pid_namespace *copy_pid_ns(unsigned long flags,
@@ -184,7 +191,11 @@
 	/* Don't allow any more processes into the pid namespace */
 	disable_pid_allocation(pid_ns);
 
-	/* Ignore SIGCHLD causing any terminated children to autoreap */
+	/*
+	 * Ignore SIGCHLD causing any terminated children to autoreap.
+	 * This speeds up the namespace shutdown, plus see the comment
+	 * below.
+	 */
 	spin_lock_irq(&me->sighand->siglock);
 	me->sighand->action[SIGCHLD - 1].sa.sa_handler = SIG_IGN;
 	spin_unlock_irq(&me->sighand->siglock);
@@ -217,15 +228,31 @@
 	}
 	read_unlock(&tasklist_lock);
 
-	/* Firstly reap the EXIT_ZOMBIE children we may have. */
+	/*
+	 * Reap the EXIT_ZOMBIE children we had before we ignored SIGCHLD.
+	 * sys_wait4() will also block until our children traced from the
+	 * parent namespace are detached and become EXIT_DEAD.
+	 */
 	do {
 		clear_thread_flag(TIF_SIGPENDING);
 		rc = sys_wait4(-1, NULL, __WALL, NULL);
 	} while (rc != -ECHILD);
 
 	/*
-	 * sys_wait4() above can't reap the TASK_DEAD children.
-	 * Make sure they all go away, see free_pid().
+	 * sys_wait4() above can't reap the EXIT_DEAD children but we do not
+	 * really care, we could reparent them to the global init. We could
+	 * exit and reap ->child_reaper even if it is not the last thread in
+	 * this pid_ns, free_pid(nr_hashed == 0) calls proc_cleanup_work(),
+	 * pid_ns can not go away until proc_kill_sb() drops the reference.
+	 *
+	 * But this ns can also have other tasks injected by setns()+fork().
+	 * Again, ignoring the user visible semantics we do not really need
+	 * to wait until they are all reaped, but they can be reparented to
+	 * us and thus we need to ensure that pid->child_reaper stays valid
+	 * until they all go away. See free_pid()->wake_up_process().
+	 *
+	 * We rely on ignored SIGCHLD, an injected zombie must be autoreaped
+	 * if reparented.
 	 */
 	for (;;) {
 		set_current_state(TASK_UNINTERRUPTIBLE);
@@ -307,7 +334,12 @@
 	return 0;
 }
 
-static void *pidns_get(struct task_struct *task)
+static inline struct pid_namespace *to_pid_ns(struct ns_common *ns)
+{
+	return container_of(ns, struct pid_namespace, ns);
+}
+
+static struct ns_common *pidns_get(struct task_struct *task)
 {
 	struct pid_namespace *ns;
 
@@ -317,21 +349,21 @@
 		get_pid_ns(ns);
 	rcu_read_unlock();
 
-	return ns;
+	return ns ? &ns->ns : NULL;
 }
 
-static void pidns_put(void *ns)
+static void pidns_put(struct ns_common *ns)
 {
-	put_pid_ns(ns);
+	put_pid_ns(to_pid_ns(ns));
 }
 
-static int pidns_install(struct nsproxy *nsproxy, void *ns)
+static int pidns_install(struct nsproxy *nsproxy, struct ns_common *ns)
 {
 	struct pid_namespace *active = task_active_pid_ns(current);
-	struct pid_namespace *ancestor, *new = ns;
+	struct pid_namespace *ancestor, *new = to_pid_ns(ns);
 
 	if (!ns_capable(new->user_ns, CAP_SYS_ADMIN) ||
-	    !nsown_capable(CAP_SYS_ADMIN))
+	    !ns_capable(current_user_ns(), CAP_SYS_ADMIN))
 		return -EPERM;
 
 	/*
@@ -351,24 +383,17 @@
 	if (ancestor != active)
 		return -EINVAL;
 
-	put_pid_ns(nsproxy->pid_ns);
-	nsproxy->pid_ns = get_pid_ns(new);
+	put_pid_ns(nsproxy->pid_ns_for_children);
+	nsproxy->pid_ns_for_children = get_pid_ns(new);
 	return 0;
 }
 
-static unsigned int pidns_inum(void *ns)
-{
-	struct pid_namespace *pid_ns = ns;
-	return pid_ns->proc_inum;
-}
-
 const struct proc_ns_operations pidns_operations = {
 	.name		= "pid",
 	.type		= CLONE_NEWPID,
 	.get		= pidns_get,
 	.put		= pidns_put,
 	.install	= pidns_install,
-	.inum		= pidns_inum,
 };
 
 static __init int pid_namespaces_init(void)