Re: [PATCH 6/6] Makes procs file writable to move all threads by tgid at once

Paul Menage
2009-08-04T19:28:54Z

On Tue, Aug 4, 2009 at 12:14 PM, Benjamin Blum<bblum@google.com> wrote:
>
> Hmm, the tasklist_lock section in fork() is entirely inside the
> read-lock. Presumably then iterating the threadgroup list to take all
> rwsems is safe from a race in which one thread escapes?
>

I think so - the write-side locking would be something like:

again:
read_lock(&tasklist_lock);
find first not-yet-locked task t
while (t != group_leader) {
if (!down_write_trylock(&t->threadgroup_stability_mutex)) {
get_task_struct(t);
read_unlock(&tasklist_lock);
down_write(&t->threadgroup_stability_mutex);
put_task_struct(t);
goto again;
}
t = t->next_thread;
}
read_unlock(&tasklist_lock);

Paul