Re: [dpdk-dev] [PATCH] vhost: Fix wrong handling of virtqueue array index

["Xie, Huawei" <huawei.xie@intel.com>]

On 10/27/2015 4:39 PM, Yuanhan Liu wrote:
> On Tue, Oct 27, 2015 at 08:24:00AM +0000, Xie, Huawei wrote:
>> On 10/27/2015 3:52 PM, Tetsuya Mukawa wrote:
>>> The patch fixes wrong handling of virtqueue array index when
>>> GET_VRING_BASE message comes.
>>> The vhost backend will receive the message per virtqueue.
>>> Also we should call a destroy callback handler when both RXQ
>>> and TXQ receives the message.
>>>
>>> Signed-off-by: Tetsuya Mukawa <mukawa@igel.co.jp>
>>> ---
>>>  lib/librte_vhost/vhost_user/virtio-net-user.c | 20 ++++++++++----------
>>>  1 file changed, 10 insertions(+), 10 deletions(-)
>>>
>>> diff --git a/lib/librte_vhost/vhost_user/virtio-net-user.c b/lib/librte_vhost/vhost_user/virtio-net-user.c
>>> index a998ad8..99c075f 100644
>>> --- a/lib/librte_vhost/vhost_user/virtio-net-user.c
>>> +++ b/lib/librte_vhost/vhost_user/virtio-net-user.c
>>> @@ -283,12 +283,10 @@ user_get_vring_base(struct vhost_device_ctx ctx,
>>>  	struct vhost_vring_state *state)
>>>  {
>>>  	struct virtio_net *dev = get_device(ctx);
>>> +	uint16_t base_idx = state->index / VIRTIO_QNUM * VIRTIO_QNUM;
>>>  
>>>  	if (dev == NULL)
>>>  		return -1;
>>> -	/* We have to stop the queue (virtio) if it is running. */
>>> -	if (dev->flags & VIRTIO_DEV_RUNNING)
>>> -		notify_ops->destroy_device(dev);
>> Hi Tetsuya:
>> I don't understand why we move it to the end of the function.
>> If we don't tell the application to remove the virtio device from the
> As you stated, he just moved it to the end of the function: it
> still does invoke notfiy_ops->destroy_device() in the end.
The problem is before calling destroy_device, we shouldn't modify the
virtio_net data structure as data plane is also using it.
>
> And the reason he moved it to the end is he want to invoke the
> callback just when the second GET_VRING_BASE message is received
> for the queue pair.
Don't get it. What issue it fixes?
>  And while thinking twice, it's not necessary,
> as we will do the "flags & VIRTIO_DEV_RUNNING" check first, it
> doesn't matter on which virt queue we invoke the callback.
>
>
> 	--yliu
>
>> data plane, then the vhost application is still operating on that
>> device, we shouldn't do anything to the virtio_net device.
>> For this case, as vhost doesn't use kickfd, it will not cause issue, but
>> i think it is best practice firstly to remove it from data plan through
>> destroy_device.
>>
>> I think we could call destroy_device the first time we receive this
>> message. Currently we don't have per queue granularity control to only
>> remove one queue from data plane.
>>
>> I am Okay to only close the kickfd for the specified queue index.
>>
>> Btw, do you meet issue with previous implementation?
>>>  
>>>  	/* Here we are safe to get the last used index */
>>>  	ops->get_vring_base(ctx, state->index, state);
>>> @@ -300,15 +298,17 @@ user_get_vring_base(struct vhost_device_ctx ctx,
>>>  	 * sent and only sent in vhost_vring_stop.
>>>  	 * TODO: cleanup the vring, it isn't usable since here.
>>>  	 */
>>> -	if (dev->virtqueue[state->index + VIRTIO_RXQ]->kickfd >= 0) {
>>> -		close(dev->virtqueue[state->index + VIRTIO_RXQ]->kickfd);
>>> -		dev->virtqueue[state->index + VIRTIO_RXQ]->kickfd = -1;
>>> -	}
>>> -	if (dev->virtqueue[state->index + VIRTIO_TXQ]->kickfd >= 0) {
>>> -		close(dev->virtqueue[state->index + VIRTIO_TXQ]->kickfd);
>>> -		dev->virtqueue[state->index + VIRTIO_TXQ]->kickfd = -1;
>>> +	if (dev->virtqueue[state->index]->kickfd >= 0) {
>>> +		close(dev->virtqueue[state->index]->kickfd);
>>> +		dev->virtqueue[state->index]->kickfd = -1;
>>>  	}
>>>  
>>> +	/* We have to stop the queue (virtio) if it is running. */
>>> +	if ((dev->flags & VIRTIO_DEV_RUNNING) &&
>>> +			(dev->virtqueue[base_idx + VIRTIO_RXQ]->kickfd == -1) &&
>>> +			(dev->virtqueue[base_idx + VIRTIO_TXQ]->kickfd == -1))
>>> +		notify_ops->destroy_device(dev);
>>> +
>>>  	return 0;
>>>  }
>>>