Re: [PATCH RESEND2] ptrace: make ptrace() fail if the tracee changed its pid unexpectedly

[Linus Torvalds]

On Tue, May 11, 2021 at 9:56 AM Oleg Nesterov <oleg@xxxxxxxxxx> wrote:
>
> This patch makes ptrace() fail in this case until debugger does wait()
> and consumes PTHREAD_EVENT_EXEC which reports old_pid.

I'm ok with the patch, just wondering which way it's supposed to come
to me. Should I just apply it directly?

That said, why this:

> +       rcu_read_lock();
> +       pid = task_pid_nr_ns(task, task_active_pid_ns(task->parent));
> +       rcu_read_unlock();

I don't see why the RCU read lock would be needed? task_pid_nr_ns()
does any required locking itself, afaik.

And even if it wasn't, this all happens with siglock held, can
anything actually change.

             Linus