Re: [PATCH] simplify/fix first_tid()

[ebiederm@xmission.com (Eric W. Biederman)]

Oleg Nesterov <oleg@tv-sign.ru> writes:

> first_tid:
>
> 	/* If nr exceeds the number of threads there is nothing todo */
> 	if (nr) {
> 		if (nr >= get_nr_threads(leader))
> 			goto done;
> 	}
>
> This is not reliable: sub-threads can exit after this check, so the
> 'for' loop below can overlap and proc_task_readdir() can return an
> already filldir'ed dirents.
>
> 	for (; pos && pid_alive(pos); pos = next_thread(pos)) {
> 		if (--nr > 0)
> 			continue;
>
> Off-by-one error, will return 'leader' when nr == 1.
>
> This patch tries to fix these problems and simplify the code.

This is better however if I read this code correctly.  It modifies
the code so the last time user space goes trough this loop
with nr > nr_threads.  Then we will walk the entire threads
list to achieve nothing.

So we really still need the nr_threads test in there so we don't
traverse the list twice everytime through readdir.

Eric