"Eric W. Biederman" wrote:
>
> Oleg Nesterov <[email protected]> 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.
This can happen only if the thread we stopped at has exited, and
some other threads have exited too, so that nr >= ->signal->count.
I think it's not worth optimizing this rare and anyway slow path.
However, you are the code author, I'll send a trivial patch which
restores this optimization if you don't change you mind.
> So we really still need the nr_threads test in there so we don't
> traverse the list twice everytime through readdir.
How so? We don't do it twice?
Oleg.
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