On 5/10/26 09:03, Simon Schippers wrote:
> On 5/10/26 00:44, Michael S. Tsirkin wrote:
>> On Sat, May 09, 2026 at 06:31:47PM +0200, Simon Schippers wrote:
>>> On 5/8/26 17:10, Simon Schippers wrote:
>>>> +static void tun_queue_purge(struct tun_struct *tun, struct tun_file
>>>> *tfile)
>>>> {
>>>> void *ptr;
>>>>
>>>> - while ((ptr = ptr_ring_consume(&tfile->tx_ring)) != NULL)
>>>> + while ((ptr = tun_ring_consume(tun, tfile)) != NULL)
>>>> tun_ptr_free(ptr);
>>>>
>>>> skb_queue_purge(&tfile->sk.sk_write_queue);
>>>
>>> Sashiko is right once again. tun_ring_consume() in tun_queue_purge()
>>> operates on a tfile that is being torn down. Its queue_index is no
>>> longer valid. After the swap in __tun_detach(), it points to the
>>> netdev subqueue of a different tfile.
>>> --> We should not wake there.
>>
>> Does it not exactly point at ntfile which is what we want to wake?
>>
>
> I see your point. But calling tun_ring_consume() as done here is
> wrong, because it does not wake if the tx_ring of the tfile
> (that is currently torn down) is empty. We could change
> tun_ring_consume() to call __tun_wake_queue()
> with consumed=0 if !ptr but I think this would slow down the consumer
> path.
>
My statement is wrong:
There is no way that the tx_ring is empty and the queue is stopped
at the same time. So we do not need to touch tun_ring_consume() and
this works just fine.
>>
>>> I will swap tun_ring_consume() with ptr_ring_consume() again and
>>> submit a v12 :)
>>
>> If so then maybe
>> netif_tx_wake_queue(netdev_get_tx_queue(tun->dev, index));
>>
>
> But we should only do this if there is space in the ntfile.
> My approach:
>
> @@ -586,12 +588,18 @@ static void __tun_detach(struct tun_file *tfile, bool
> clean)
> BUG_ON(index >= tun->numqueues);
>
> rcu_assign_pointer(tun->tfiles[index],
> tun->tfiles[tun->numqueues - 1]);
> ntfile = rtnl_dereference(tun->tfiles[index]);
> + spin_lock(&ntfile->tx_ring.consumer_lock);
> ntfile->queue_index = index;
> ntfile->xdp_rxq.queue_index = index;
> + ntfile->cons_cnt = 0;
> + if (__ptr_ring_empty(&ntfile->tx_ring)) {
> + netif_wake_subqueue(tun->dev, index);
> + }
> + spin_unlock(&ntfile->tx_ring.consumer_lock);
> rcu_assign_pointer(tun->tfiles[tun->numqueues - 1],
> NULL);
>
> ntfile->cons_cnt is unvalid, because the new queue might not be stopped.
> That is the reason why I reset it to 0.
However, I still prefer this approach because the code is easier to
understand.
