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

[Stanislav Kinsbursky]

17.10.2012 17:57, Eric Dumazet ÐÐÑÐÑ:
> 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 Or else another thread can read outdated informations...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;

Sorry, but I don't understand what races you are talking about.
Could you specify, please?

--
Best regards,
Stanislav Kinsbursky
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