| Re: [RFC PATCH v2] posix timers: allocate timer id per task [message #48430 is a reply to message #48428] |
Wed, 17 October 2012 14:26  |
Stanislav Kinsbursky
Messages: 683
Registered: October 2011
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Senior Member |
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17.10.2012 17:57, Eric Dumazet пишет:
> 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(¤t->sighand->siglock);
> new_timer->it_signal = current->signal;
> list_add(&new_timer->list, ¤t->signal->posix_timers);
> spin_unlock_irq(¤t->sighand->siglock);
>
> Or else another thread can read outdated informations...
>
>
> spin_lock_irq(¤t->sighand->siglock);
> list_add(&new_timer->list, ¤t->signal->posix_timers);
> spin_unlock_irq(¤t->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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