Re: [take21 1/4] kevent: Core files.

Eric Dumazet
2006-10-28T12:36:36Z

Evgeniy Polyakov a e'crit :
> On Sat, Oct 28, 2006 at 12:28:12PM +0200, Eric Dumazet (dada1@cosmosbay.com) wrote:
>>
>> I really dont understand how you manage to queue multiple kevents in the
>> 'overflow list'. You just queue one kevent at most. What am I missing ?
>
> There is no overflow list - it is a pointer to the first kevent in the
> ready queue, which was not put into ring buffer. It is an optimisation,
> which allows to not search for that position each time new event should
> be placed into the buffer, when it starts to have an empty slot.

This overflow list (you may call it differently, but still it IS a list), is
not complete. I feel you add it just to make me happy, but I am not (yet :) )

For example, you make no test at kevent_finish_user_complete() time.

Obviously, you can have a dangling pointer, and crash your box in certain
conditions.

static void kevent_finish_user_complete(struct kevent *k, int deq)
{
struct kevent_user *u = k->user;
unsigned long flags;

if (deq)
kevent_dequeue(k);

spin_lock_irqsave(&u->ready_lock, flags);
if (k->flags & KEVENT_READY) {
+ if (u->overflow_event == k) {
+ /* MUST do something to change u->overflow_kevent */
+ }
list_del(&k->ready_entry);
k->flags &= ~KEVENT_READY;
u->ready_num--;
}
spin_unlock_irqrestore(&u->ready_lock, flags);

kevent_user_put(u);
call_rcu(&k->rcu_head, kevent_free_rcu);
}

Eric