linux-kernel - Re: [PATCH 2/2] virtio_ring: fix complaint by sparse

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Date:   Tue, 22 Nov 2016 16:16:54 +0100
From:   Thomas Huth <thuth@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>,
        Gonglei <arei.gonglei@...wei.com>
Cc:     david@...son.dropbear.id.au, linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH 2/2] virtio_ring: fix complaint by sparse

On 22.11.2016 16:04, Michael S. Tsirkin wrote:
> On Tue, Nov 22, 2016 at 01:51:50PM +0800, Gonglei wrote:
>>  # make C=2 CF="-D__CHECK_ENDIAN__" ./drivers/virtio/
>>
>> drivers/virtio/virtio_ring.c:423:19: warning: incorrect type in assignment (different base types)
>> drivers/virtio/virtio_ring.c:423:19:    expected unsigned int [unsigned] [assigned] i
>> drivers/virtio/virtio_ring.c:423:19:    got restricted __virtio16 [usertype] next
>> drivers/virtio/virtio_ring.c:423:19: warning: incorrect type in assignment (different base types)
>> drivers/virtio/virtio_ring.c:423:19:    expected unsigned int [unsigned] [assigned] i
>> drivers/virtio/virtio_ring.c:423:19:    got restricted __virtio16 [usertype] next
>> drivers/virtio/virtio_ring.c:423:19: warning: incorrect type in assignment (different base types)
>> drivers/virtio/virtio_ring.c:423:19:    expected unsigned int [unsigned] [assigned] i
>> drivers/virtio/virtio_ring.c:423:19:    got restricted __virtio16 [usertype] next
>> drivers/virtio/virtio_ring.c:604:39: warning: incorrect type in initializer (different base types)
>> drivers/virtio/virtio_ring.c:604:39:    expected unsigned short [unsigned] [usertype] nextflag
>> drivers/virtio/virtio_ring.c:604:39:    got restricted __virtio16
>> drivers/virtio/virtio_ring.c:612:33: warning: restricted __virtio16 degrades to integer
>>
>> Signed-off-by: Gonglei <arei.gonglei@...wei.com>
>> ---
>>  drivers/virtio/virtio_ring.c | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
>> index 489bfc6..d2863c3 100644
>> --- a/drivers/virtio/virtio_ring.c
>> +++ b/drivers/virtio/virtio_ring.c
>> @@ -420,7 +420,7 @@ static inline int virtqueue_add(struct virtqueue *_vq,
>>  		if (i == err_idx)
>>  			break;
>>  		vring_unmap_one(vq, &desc[i]);
>> -		i = vq->vring.desc[i].next;
>> +		i = virtio16_to_cpu(_vq->vdev, vq->vring.desc[i].next);
>>  	}
>>  
>>  	vq->vq.num_free += total_sg;
[...]
> Wow are you saying endian-ness is all wrong for the next field?
> How do things ever work then?

The above code is only in the error cleanup path (after the
"unmap_release" label, introduced by commit 780bc7903), so it likely has
never been exercised in the field.
I think Gonlei's patch is right, there should be a virtio16_to_cpu() here.

 Thomas