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SubjectRe: [PATCH] kernel: release ptraced tasks before zap_pid_ns_processes
Oops, Al is here by mistake. Sorry about that.

On Wed, Jan 02, 2019 at 12:59:39PM -0800, Andrei Vagin wrote:
> Currently, exit_ptrace() adds all ptraced tasks in a dead list, than
> zap_pid_ns_processes() waits all tasks in a current pid ns, and only
> then tasks from the dead list are released.
>
> zap_pid_ns_processes() can stuck on waiting tasks from the dead list. In
> this case, we will have one unkillable process with one or more dead
> children.
>
> Cc: Oleg Nesterov <oleg@redhat.com>
> Cc: "Eric W. Biederman" <ebiederm@xmission.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Andrei Vagin <avagin@gmail.com>
> ---
> kernel/exit.c | 15 +++++++++++----
> 1 file changed, 11 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/exit.c b/kernel/exit.c
> index 0e21e6d21f35..ccaa6f6549ba 100644
> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -664,9 +664,6 @@ static void forget_original_parent(struct task_struct *father,
> {
> struct task_struct *p, *t, *reaper;
>
> - if (unlikely(!list_empty(&father->ptraced)))
> - exit_ptrace(father, dead);
> -
> /* Can drop and reacquire tasklist_lock */
> reaper = find_child_reaper(father);
> if (list_empty(&father->children))
> @@ -705,8 +702,18 @@ static void exit_notify(struct task_struct *tsk, int group_dead)
> LIST_HEAD(dead);
>
> write_lock_irq(&tasklist_lock);
> - forget_original_parent(tsk, &dead);
> + if (unlikely(!list_empty(&tsk->ptraced)))
> + exit_ptrace(tsk, &dead);
> + write_unlock_irq(&tasklist_lock);
> +
> + /* Ptraced tasks have to be released before zap_pid_ns_processes(). */
> + list_for_each_entry_safe(p, n, &dead, ptrace_entry) {
> + list_del_init(&p->ptrace_entry);
> + release_task(p);
> + }
>
> + write_lock_irq(&tasklist_lock);
> + forget_original_parent(tsk, &dead);
> if (group_dead)
> kill_orphaned_pgrp(tsk->group_leader, NULL);
>
> --
> 2.17.2
>

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