The patch titled Subject: pidns: guarantee that the pidns init will be the last pidns process reaped has been added to the -mm tree. Its filename is pidns-guarantee-that-the-pidns-init-will-be-the-last-pidns-process-reaped.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/SubmitChecklist when testing your code *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ From: Eric W. Biederman <ebiederm@xxxxxxxxxxxx> Subject: pidns: guarantee that the pidns init will be the last pidns process reaped Today we have a twofold bug. Sometimes release_task on pid == 1 in a pid namespace can run before other processes in a pid namespace have had release task called. With the result that pid_ns_release_proc can be called before the last proc_flus_task() is done using upid->ns->proc_mnt, resulting in the use of a stale pointer. This same set of circumstances can lead to waitpid(...) returning for a processes started with clone(CLONE_NEWPID) before the every process in the pid namespace has actually exited. To fix this modify zap_pid_ns_processess wait until all other processes in the pid namespace have exited, even EXIT_DEAD zombies. The delay_group_leader and related tests ensure that the thread gruop leader will be the last thread of a process group to be reaped, or to become EXIT_DEAD and self reap. With the change to zap_pid_ns_processes we get the guarantee that pid == 1 in a pid namespace will be the last task that release_task is called on. With pid == 1 being the last task to pass through release_task pid_ns_release_proc can no longer be called too early nor can wait return before all of the EXIT_DEAD tasks in a pid namespace have exited. Signed-off-by: Eric W. Biederman <ebiederm@xxxxxxxxxxxx> Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx> Cc: Louis Rilling <louis.rilling@xxxxxxxxxxx> Cc: Mike Galbraith <efault@xxxxxx> Acked-by: Pavel Emelyanov <xemul@xxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- kernel/exit.c | 14 +++++++++++++- kernel/pid_namespace.c | 20 ++++++++++++++++++++ 2 files changed, 33 insertions(+), 1 deletion(-) diff -puN kernel/exit.c~pidns-guarantee-that-the-pidns-init-will-be-the-last-pidns-process-reaped kernel/exit.c --- a/kernel/exit.c~pidns-guarantee-that-the-pidns-init-will-be-the-last-pidns-process-reaped +++ a/kernel/exit.c @@ -64,7 +64,6 @@ static void exit_mm(struct task_struct * static void __unhash_process(struct task_struct *p, bool group_dead) { nr_threads--; - detach_pid(p, PIDTYPE_PID); if (group_dead) { detach_pid(p, PIDTYPE_PGID); detach_pid(p, PIDTYPE_SID); @@ -72,7 +71,20 @@ static void __unhash_process(struct task 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(p)->child_reaper == parent) && + list_empty(&parent->children) && + (parent->flags & PF_EXITING)) + wake_up_process(parent); + } } + detach_pid(p, PIDTYPE_PID); list_del_rcu(&p->thread_group); } diff -puN kernel/pid_namespace.c~pidns-guarantee-that-the-pidns-init-will-be-the-last-pidns-process-reaped kernel/pid_namespace.c --- a/kernel/pid_namespace.c~pidns-guarantee-that-the-pidns-init-will-be-the-last-pidns-process-reaped +++ a/kernel/pid_namespace.c @@ -184,11 +184,31 @@ void zap_pid_ns_processes(struct pid_nam } read_unlock(&tasklist_lock); + /* Firstly reap the EXIT_ZOMBIE children we may have. */ 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 __unhash_process(). + */ + for (;;) { + bool need_wait = false; + + read_lock(&tasklist_lock); + if (!list_empty(¤t->children)) { + __set_current_state(TASK_UNINTERRUPTIBLE); + need_wait = true; + } + read_unlock(&tasklist_lock); + + if (!need_wait) + break; + schedule(); + } + if (pid_ns->reboot) current->signal->group_exit_code = pid_ns->reboot; _ Subject: Subject: pidns: guarantee that the pidns init will be the last pidns process reaped Patches currently in -mm which might be from ebiederm@xxxxxxxxxxxx are linux-next.patch pidns-guarantee-that-the-pidns-init-will-be-the-last-pidns-process-reaped.patch pidns-find_new_reaper-can-no-longer-switch-to-init_pid_nschild_reaper.patch c-r-fcntl-add-f_getowner_uids-option.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html