Re: [PATCH 1/1] ovpn: tcp - defer TX from softirq to workqueue

[Antonio Quartulli]

Hi,

On 01/05/2026 16:54, Dao Zhong Ma wrote:
> ovpn_tcp_send_skb() holds sk->sk_lock.slock while performing the full TCP
> send in softirq context. This can hold the spinlock for a long time
> (large skb), blocking lock_sock() users. This can starve the RCU GP

Are you sure that the stall is triggered by just processing 1 large skb?

> kthread and trigger RCU stalls warnings and hung tasks.

Can you trigger the stall/warning easily?
Any steps to reproduce?



> Defer the TCP send operation to process context:
> - In interrupt context, only enqueue the skb under the spinlock
>    schedule tcp_tx_work.
> - In process context, dequeue and flush the send queue under lock_sock()
>
> This reduces the softirq critical section to a short duration, allowing
> lock_sock() users to make progress and preventing RCU stalls.
>
> Signed-off-by: Dao Zhong Ma <cz1346219@xxxxxxxxx>

As Jakub pointed out, this is breaking the selftests, therefore you 
should first double check what's going wrong.

On top of that, could you please run some performance tests? I think 
this is going to hit quite a penalty.

Especially if you have multiple peers and you defer all their traffic to 
the same workqueue.

Regards,



--
Antonio Quartulli
OpenVPN Inc.