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Re: [RFC PATCH v2] posix timers: allocate timer id per task [message #48428 is a reply to message #48426] Wed, 17 October 2012 13:57 Go to previous messageGo to previous message
Eric Dumazet is currently offline  Eric Dumazet
Messages: 36
Registered: July 2006
Member
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Or else another thread can read outdated informations...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;

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