Commit af4b8a83 authored by Eric W. Biederman's avatar Eric W. Biederman
Browse files

pidns: Wait in zap_pid_ns_processes until pid_ns->nr_hashed == 1 



Looking at pid_ns->nr_hashed is a bit simpler and it works for
disjoint process trees that an unshare or a join of a pid_namespace
may create.

Acked-by: default avatar"Serge E. Hallyn" <serge@hallyn.com>
Signed-off-by: default avatar"Eric W. Biederman" <ebiederm@xmission.com>
parent 5e1182de

kernel/exit.c

+0 −12
Original line number Diff line number Diff line
@@ -72,18 +72,6 @@ static void __unhash_process(struct task_struct *p, bool group_dead) 
		list_del_rcu(&p->tasks);

		list_del_init(&p->sibling);

		__this_cpu_dec(process_counts);

		/*

		 * If we are the last child process in a pid namespace to be

		 * reaped, notify the reaper sleeping zap_pid_ns_processes().

		 */

		if (IS_ENABLED(CONFIG_PID_NS)) {

			struct task_struct *parent = p->real_parent;



			if ((task_active_pid_ns(parent)->child_reaper == parent) &&

			    list_empty(&parent->children) &&

			    (parent->flags & PF_EXITING))

				wake_up_process(parent);

		}

	}

	list_del_rcu(&p->thread_group);

}

kernel/pid.c

+13 −3
Original line number Diff line number Diff line
@@ -273,10 +273,20 @@ void free_pid(struct pid *pid) 
	spin_lock_irqsave(&pidmap_lock, flags);

	for (i = 0; i <= pid->level; i++) {

		struct upid *upid = pid->numbers + i;

		struct pid_namespace *ns = upid->ns;

		hlist_del_rcu(&upid->pid_chain);

		if (--upid->ns->nr_hashed == 0) {

			upid->ns->nr_hashed = -1;

			schedule_work(&upid->ns->proc_work);

		switch(--ns->nr_hashed) {

		case 1:

			/* When all that is left in the pid namespace

			 * is the reaper wake up the reaper.  The reaper

			 * may be sleeping in zap_pid_ns_processes().

			 */

			wake_up_process(ns->child_reaper);

			break;

		case 0:

			ns->nr_hashed = -1;

			schedule_work(&ns->proc_work);

			break;

		}

	}

	spin_unlock_irqrestore(&pidmap_lock, flags);

kernel/pid_namespace.c

+4 −11
Original line number Diff line number Diff line
@@ -217,22 +217,15 @@ void zap_pid_ns_processes(struct pid_namespace *pid_ns) 


	/*

	 * sys_wait4() above can't reap the TASK_DEAD children.

	 * Make sure they all go away, see __unhash_process().

	 * Make sure they all go away, see free_pid().

	 */

	for (;;) {

		bool need_wait = false;



		read_lock(&tasklist_lock);

		if (!list_empty(&current->children)) {

			__set_current_state(TASK_UNINTERRUPTIBLE);

			need_wait = true;

		}

		read_unlock(&tasklist_lock);



		if (!need_wait)

		set_current_state(TASK_UNINTERRUPTIBLE);

		if (pid_ns->nr_hashed == 1)

			break;

		schedule();

	}

	__set_current_state(TASK_RUNNING);



	if (pid_ns->reboot)

		current->signal->group_exit_code = pid_ns->reboot;