netdev - Re: [PATCH 1/6] vhost: allow device that does not depend on vhost worker

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Message-ID: <21e1bfbf-4b0c-5a73-6fdd-a58c43c733ea@redhat.com>
Date:   Tue, 2 Jun 2020 15:04:08 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        rob.miller@...adcom.com, lingshan.zhu@...el.com,
        eperezma@...hat.com, lulu@...hat.com, shahafs@...lanox.com,
        hanand@...inx.com, mhabets@...arflare.com, gdawar@...inx.com,
        saugatm@...inx.com, vmireyno@...vell.com,
        zhangweining@...jie.com.cn, eli@...lanox.com
Subject: Re: [PATCH 1/6] vhost: allow device that does not depend on vhost
 worker


On 2020/6/2 下午1:01, Michael S. Tsirkin wrote:
> On Fri, May 29, 2020 at 04:02:58PM +0800, Jason Wang wrote:
>> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
>> index d450e16c5c25..70105e045768 100644
>> --- a/drivers/vhost/vhost.c
>> +++ b/drivers/vhost/vhost.c
>> @@ -166,11 +166,16 @@ static int vhost_poll_wakeup(wait_queue_entry_t *wait, unsigned mode, int sync,
>>   			     void *key)
>>   {
>>   	struct vhost_poll *poll = container_of(wait, struct vhost_poll, wait);
>> +	struct vhost_work *work = &poll->work;
>>   
>>   	if (!(key_to_poll(key) & poll->mask))
>>   		return 0;
>>   
>> -	vhost_poll_queue(poll);
>> +	if (!poll->dev->use_worker)
>> +		work->fn(work);
>> +	else
>> +		vhost_poll_queue(poll);
>> +
>>   	return 0;
>>   }
>>
> So a wakeup function wakes up eventfd directly.
>
> What if user supplies e.g. the same eventfd as ioeventfd?
>
> Won't this cause infinite loops?


I'm not sure I get this.

This basically calls handle_vq directly when eventfd is woken up. The 
infinite loops can only happen when handle_vq() tries to write to 
ioeventfd itslef which should be a bug of the device.

Thanks


>