linux-kernel - Re: [PATCH net 3/4] virtio-net: reset num

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Date:   Tue, 22 May 2018 11:36:18 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net 3/4] virtio-net: reset num_buf to 1 after linearizing
 packet



On 2018年05月21日 22:59, Michael S. Tsirkin wrote:
> On Mon, May 21, 2018 at 04:35:05PM +0800, Jason Wang wrote:
>> If we successfully linearize the packets, num_buf were set to zero
>> which was wrong since we now have only 1 buffer to be used for e.g in
>> the error path of receive_mergeable(). Zero num_buf will lead the code
>> try to pop the buffers of next packet and drop it. Fixing this by set
>> num_buf to 1 if we successfully linearize the packet.
>>
>> Fixes: 4941d472bf95 ("virtio-net: do not reset during XDP set")
>> Signed-off-by: Jason Wang <jasowang@...hat.com>
>> ---
>>   drivers/net/virtio_net.c | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>> index 6260d65..165a922 100644
>> --- a/drivers/net/virtio_net.c
>> +++ b/drivers/net/virtio_net.c
>> @@ -722,6 +722,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>>   						      &len);
>>   			if (!xdp_page)
>>   				goto err_xdp;
>> +			num_buf = 1;
> So this is tweaked here for the benefit of err_skb below.
> That's confusing and we won't remember to change it
> if we change the error handling.
>
> How about fixing the error path?
>
>
> -        while (--num_buf) {
> +        while (num_buf-- > 1) {
>
> Seems more robust to me.

Looks good, will do this in V2.

Thanks

>
>>   			offset = VIRTIO_XDP_HEADROOM;
>>   		} else {
>>   			xdp_page = page;
>> -- 
>> 2.7.4