netdev - Re: [PATCH net-next v5 4/4] virtio-net: support rx netdim

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Message-ID: <6f78d5e0-a8a8-463e-938c-9a9b49cf106f@linux.alibaba.com>
Date: Thu, 30 Nov 2023 20:09:38 +0800
From: Heng Qi <hengqi@...ux.alibaba.com>
To: Paolo Abeni <pabeni@...hat.com>,
 virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org
Cc: jasowang@...hat.com, mst@...hat.com, kuba@...nel.org,
 edumazet@...gle.com, davem@...emloft.net, hawk@...nel.org,
 john.fastabend@...il.com, ast@...nel.org, horms@...nel.org,
 xuanzhuo@...ux.alibaba.com, yinjun.zhang@...igine.com
Subject: Re: [PATCH net-next v5 4/4] virtio-net: support rx netdim



在 2023/11/30 下午5:33, Paolo Abeni 写道:
> On Mon, 2023-11-27 at 10:55 +0800, Heng Qi wrote:
>> @@ -4738,11 +4881,14 @@ static void remove_vq_common(struct virtnet_info *vi)
>>   static void virtnet_remove(struct virtio_device *vdev)
>>   {
>>   	struct virtnet_info *vi = vdev->priv;
>> +	int i;
>>   
>>   	virtnet_cpu_notif_remove(vi);
>>   
>>   	/* Make sure no work handler is accessing the device. */
>>   	flush_work(&vi->config_work);
>> +	for (i = 0; i < vi->max_queue_pairs; i++)
>> +		cancel_work(&vi->rq[i].dim.work);
> If the dim work is still running here, what prevents it from completing
> after the following unregister/free netdev?

Yes, no one here is trying to stop it, the situation is like 
unregister/free netdev
when rss are being set, so I think this is ok.

>
> It looks like you want need to call cancel_work_sync here?

In v4, Yinjun Zhang mentioned that _sync() can cause deadlock[1].
Therefore, cancel_work() is used here instead of cancel_work_sync() to 
avoid possible deadlock.

[1] 
https://lore.kernel.org/all/20231122092939.1005591-1-yinjun.zhang@corigine.com/

>
> Additionally the later remove_vq_common() will needless call
> cancel_work() again;

Yes. remove_vq_common() now does not call cancel_work().

> possibly is better to consolidate a single (sync)
> call there.

Do you mean add it in virtnet_freeze()?
cancel_work() has existed in the path virtnet_freeze() -> 
virtnet_freeze_down() -> virtnet_close().

Thanks!

>
> Cheers,
>
> Paolo