On Tue, Jan 08, 2019 at 05:50:43PM +0100, Oleg Nesterov wrote:
> Sorry for delay, vacation,
>
> On 01/02, Andrei Vagin wrote:
> >
> > 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.
>
> Thanks!
>
> > --- 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);
>
> How about a different fix below? It avoids additional
> write_lock/unlock(tasklist),
> and another list_for_each_entry_safe(dead) loop is called only if it is
> actually
> needed.
>
> Or I missed something?
No, you don't. The patch looks really nice. Thanks!
BTW: We probably need to add the "Fixes:" tag, but I am not sure to which
commit, it looks like the issue is here for years.
Acked-by: Andrei Vagin <[email protected]>
>
> Oleg.
>
>
> --- x/kernel/exit.c
> +++ x/kernel/exit.c
> @@ -558,12 +558,14 @@ static struct task_struct *find_alive_th
> return NULL;
> }
>
> -static struct task_struct *find_child_reaper(struct task_struct *father)
> +static struct task_struct *find_child_reaper(struct task_struct *father,
> + struct list_head *dead)
> __releases(&tasklist_lock)
> __acquires(&tasklist_lock)
> {
> struct pid_namespace *pid_ns = task_active_pid_ns(father);
> struct task_struct *reaper = pid_ns->child_reaper;
> + struct task_struct *p, *n;
>
> if (likely(reaper != father))
> return reaper;
> @@ -579,6 +581,11 @@ static struct task_struct *find_child_re
> panic("Attempted to kill init! exitcode=0x%08x\n",
> father->signal->group_exit_code ?: father->exit_code);
> }
> +
> + list_for_each_entry_safe(p, n, &dead, ptrace_entry) {
> + list_del_init(&p->ptrace_entry);
> + release_task(p);
> + }
> zap_pid_ns_processes(pid_ns);
> write_lock_irq(&tasklist_lock);
>
> @@ -668,7 +675,7 @@ static void forget_original_parent(struc
> exit_ptrace(father, dead);
>
> /* Can drop and reacquire tasklist_lock */
> - reaper = find_child_reaper(father);
> + reaper = find_child_reaper(father, dead);
> if (list_empty(&father->children))
> return;
>
>
