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: "Serge E. Hallyn" <serge@hallyn.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

1 files changed, 4 insertions, 11 deletions

diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
index 84591cfeefc1..3cc29b830e9e 100644
--- a/kernel/pid_namespace.c
+++ b/kernel/pid_namespace.c
@@ -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;