Merge branch 'akpm' (patchbomb from Andrew)

Merge first patchbomb from Andrew Morton:
 - a few minor cifs fixes
 - dma-debug upadtes
 - ocfs2
 - slab
 - about half of MM
 - procfs
 - kernel/exit.c
 - panic.c tweaks
 - printk upates
 - lib/ updates
 - checkpatch updates
 - fs/binfmt updates
 - the drivers/rtc tree
 - nilfs
 - kmod fixes
 - more kernel/exit.c
 - various other misc tweaks and fixes

* emailed patches from Andrew Morton <akpm@linux-foundation.org>: (190 commits)
  exit: pidns: fix/update the comments in zap_pid_ns_processes()
  exit: pidns: alloc_pid() leaks pid_namespace if child_reaper is exiting
  exit: exit_notify: re-use "dead" list to autoreap current
  exit: reparent: call forget_original_parent() under tasklist_lock
  exit: reparent: avoid find_new_reaper() if no children
  exit: reparent: introduce find_alive_thread()
  exit: reparent: introduce find_child_reaper()
  exit: reparent: document the ->has_child_subreaper checks
  exit: reparent: s/while_each_thread/for_each_thread/ in find_new_reaper()
  exit: reparent: fix the cross-namespace PR_SET_CHILD_SUBREAPER reparenting
  exit: reparent: fix the dead-parent PR_SET_CHILD_SUBREAPER reparenting
  exit: proc: don't try to flush /proc/tgid/task/tgid
  exit: release_task: fix the comment about group leader accounting
  exit: wait: drop tasklist_lock before psig->c* accounting
  exit: wait: don't use zombie->real_parent
  exit: wait: cleanup the ptrace_reparented() checks
  usermodehelper: kill the kmod_thread_locker logic
  usermodehelper: don't use CLONE_VFORK for ____call_usermodehelper()
  fs/hfs/catalog.c: fix comparison bug in hfs_cat_keycmp
  nilfs2: fix the nilfs_iget() vs. nilfs_new_inode() races
  ...

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);