[Devel] Re: [RFC PATCH v2] posix timers: allocate timer id per task

[Eric Dumazet]

On Wed, 2012-10-17 at 17:18 +0400, Stanislav Kinsbursky wrote:

> +static int posix_timer_add(struct k_itimer *timer)
> +{
> +     struct signal_struct *sig = current->signal;
> +     int next_free_id = sig->posix_timer_id;
> +     struct hlist_head *head;
> +     int ret = -ENOENT;
> +
> +     do {
> +             spin_lock(&hash_lock);
> +             head = &posix_timers_hashtable[hash(sig, sig->posix_timer_id)];
> +             if (__posix_timers_find(head, sig, sig->posix_timer_id) == 
> NULL) {
> +                     hlist_add_head_rcu(&timer->t_hash, head);

Hmm...

> +                     ret = sig->posix_timer_id++;
> +             } else {
> +                     if (++sig->posix_timer_id < 0)
> +                             sig->posix_timer_id = 0;
> +                     if (sig->posix_timer_id == next_free_id)
> +                             ret = -EAGAIN;
> +             }
> +             spin_unlock(&hash_lock);
> +     } while (ret == -ENOENT);
> +     return ret;
> +}
> +

You probably need to add a rcu_assign_pointer() or smp_wmb() before
the :

new_timer->it_signal = current->signal;

in the following block :

        spin_lock_irq(&current->sighand->siglock);
        new_timer->it_signal = current->signal;
        list_add(&new_timer->list, &current->signal->posix_timers);
        spin_unlock_irq(&current->sighand->siglock);

Or else another thread can read outdated informations...


        spin_lock_irq(&current->sighand->siglock);
        list_add(&new_timer->list, &current->signal->posix_timers);
        spin_unlock_irq(&current->sighand->siglock);
        smp_wmb();
        new_timer->it_signal = current->signal;


_______________________________________________
Devel mailing list
Devel@openvz.org
https://openvz.org/mailman/listinfo/devel