Re: [PATCH] simplify/fix first_tid()

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

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

> "Eric W. Biederman" wrote:
>> 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?

In general user space does.  Because a read of 0 bytes signifies
the end of a directory.

So we have 2 trips through proc_task_readdir initiated by user
space.

Eric