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-rw-r--r--kernel/pid_namespace.c28
1 files changed, 24 insertions, 4 deletions
diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
index db95d8eb761b..bc6d6a89b6e6 100644
--- a/kernel/pid_namespace.c
+++ b/kernel/pid_namespace.c
@@ -190,7 +190,11 @@ void zap_pid_ns_processes(struct pid_namespace *pid_ns)
/* 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);
@@ -223,15 +227,31 @@ void zap_pid_ns_processes(struct pid_namespace *pid_ns)
}
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);