From: Eric W. Biederman Date: Fri, 28 Feb 2020 22:29:12 +0000 (-0600) Subject: pid: Improve the comment about waiting in zap_pid_ns_processes X-Git-Tag: v5.10.7~2820^2~3^2 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=af9fe6d607c9f456fb6c1cb87e1dc66a43846efd;p=platform%2Fkernel%2Flinux-rpi.git pid: Improve the comment about waiting in zap_pid_ns_processes Oleg wrote a very informative comment, but with the removal of proc_cleanup_work it is no longer accurate. Rewrite the comment so that it only talks about the details that are still relevant, and hopefully is a little clearer. Signed-off-by: "Eric W. Biederman" --- diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c index 318fcc6..01f8ba3 100644 --- a/kernel/pid_namespace.c +++ b/kernel/pid_namespace.c @@ -224,20 +224,27 @@ void zap_pid_ns_processes(struct pid_namespace *pid_ns) } while (rc != -ECHILD); /* - * kernel_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(pid_allocated == 0) calls proc_cleanup_work(), - * pid_ns can not go away until proc_kill_sb() drops the reference. + * kernel_wait4() misses EXIT_DEAD children, and EXIT_ZOMBIE + * process whose parents processes are outside of the pid + * namespace. Such processes are created with setns()+fork(). * - * 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(). + * If those EXIT_ZOMBIE processes are not reaped by their + * parents before their parents exit, they will be reparented + * to pid_ns->child_reaper. Thus pidns->child_reaper needs to + * stay valid until they all go away. * - * We rely on ignored SIGCHLD, an injected zombie must be autoreaped - * if reparented. + * The code relies on the the pid_ns->child_reaper ignoring + * SIGCHILD to cause those EXIT_ZOMBIE processes to be + * autoreaped if reparented. + * + * Semantically it is also desirable to wait for EXIT_ZOMBIE + * processes before allowing the child_reaper to be reaped, as + * that gives the invariant that when the init process of a + * pid namespace is reaped all of the processes in the pid + * namespace are gone. + * + * Once all of the other tasks are gone from the pid_namespace + * free_pid() will awaken this task. */ for (;;) { set_current_state(TASK_INTERRUPTIBLE);