On 11/15, Yonghong Song wrote:
>
> On 11/14/23 11:32 AM, Oleg Nesterov wrote:
> >@@ -70,15 +70,13 @@ static struct task_struct *task_group_seq_get_next(struct bpf_iter_seq_task_comm
> > return NULL;
> > retry:
> >- task = next_thread(task);
> >+ task = __next_thread(task);
> >+ if (!task)
> >+ return NULL;
> > next_tid = __task_pid_nr_ns(task, PIDTYPE_PID, common->ns);
> >- if (!next_tid || next_tid == common->pid) {
> >- /* Run out of tasks of a process. The tasks of a
> >- * thread_group are linked as circular linked list.
> >- */
> >- return NULL;
> >- }
> >+ if (!next_tid)
> >+ goto retry;
>
> Look at the code. Looks like next_tid should never be 0
...
> pid_t __task_pid_nr_ns(struct task_struct *task, enum pid_type type,
> struct pid_namespace *ns)
> {
> pid_t nr = 0;
>
> rcu_read_lock();
> if (!ns)
> ns = task_active_pid_ns(current);
> nr = pid_nr_ns(rcu_dereference(*task_pid_ptr(task, type)), ns);
^^^^^^^^^^^^^^^^^^^^^^^^^
Please note that task_pid_ptr(task, type)) can return NULL if this
task has already exited and called detach_pid().
detach_pid() does __change_pid(task, type, NULL), please note the
*pid_ptr = new; // NULL in this case
assignment in __change_pid().
IOW. The problem is not that ns can change, the problem is that
task->thread_pid (and other pid links) can be NULL, and in this
case pid_nr_ns() returns zero.
This code should be rewritten from the very beginning, it should
not rely on pid_nr. If nothing else common->pid and/or pid_visiting
can be reused. But currently my only concern is next_thread().
> Other than above, the change looks good to me.
Thanks for review!
Oleg.
