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

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Date:   Tue, 22 Nov 2016 09:25:29 -0800
From:   Andy Lutomirski <luto@...capital.net>
To:     Thomas Huth <thuth@...hat.com>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        Gonglei <arei.gonglei@...wei.com>, david@...son.dropbear.id.au,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Linux Virtualization <virtualization@...ts.linux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH 2/2] virtio_ring: fix complaint by sparse

On Tue, Nov 22, 2016 at 7:16 AM, Thomas Huth <thuth@...hat.com> wrote:
> 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.

Agreed.

>
>  Thomas
>
>



-- 
Andy Lutomirski
AMA Capital Management, LLC