linux-kernel - Re: [PATCH 1/2] virtio_ring: Fix error reporting in virtqueue

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Message-ID: <434ab5d7-313c-4835-b0d9-47a1eec31551@redhat.com>
Date: Wed, 21 May 2025 09:25:59 +0200
From: Laurent Vivier <lvivier@...hat.com>
To: Jason Wang <jasowang@...hat.com>
Cc: linux-kernel@...r.kernel.org, "Michael S. Tsirkin" <mst@...hat.com>,
 netdev@...r.kernel.org, Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Subject: Re: [PATCH 1/2] virtio_ring: Fix error reporting in virtqueue_resize

On 21/05/2025 03:00, Jason Wang wrote:
> On Tue, May 20, 2025 at 7:05 PM Laurent Vivier <lvivier@...hat.com> wrote:
>>
>> The virtqueue_resize() function was not correctly propagating error codes
>> from its internal resize helper functions, specifically
>> virtqueue_resize_packet() and virtqueue_resize_split(). If these helpers
>> returned an error, but the subsequent call to virtqueue_enable_after_reset()
>> succeeded, the original error from the resize operation would be masked.
>> Consequently, virtqueue_resize() could incorrectly report success to its
>> caller despite an underlying resize failure.
>>
>> This change restores the original code behavior:
>>
>>         if (vdev->config->enable_vq_after_reset(_vq))
>>                 return -EBUSY;
>>
>>         return err;
>>
>> Fix: commit ad48d53b5b3f ("virtio_ring: separate the logic of reset/enable from virtqueue_resize")
>> Cc: xuanzhuo@...ux.alibaba.com
>> Signed-off-by: Laurent Vivier <lvivier@...hat.com>
>> ---
>>   drivers/virtio/virtio_ring.c | 8 ++++++--
>>   1 file changed, 6 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
>> index b784aab66867..4397392bfef0 100644
>> --- a/drivers/virtio/virtio_ring.c
>> +++ b/drivers/virtio/virtio_ring.c
>> @@ -2797,7 +2797,7 @@ int virtqueue_resize(struct virtqueue *_vq, u32 num,
>>                       void (*recycle_done)(struct virtqueue *vq))
>>   {
>>          struct vring_virtqueue *vq = to_vvq(_vq);
>> -       int err;
>> +       int err, err_reset;
>>
>>          if (num > vq->vq.num_max)
>>                  return -E2BIG;
>> @@ -2819,7 +2819,11 @@ int virtqueue_resize(struct virtqueue *_vq, u32 num,
>>          else
>>                  err = virtqueue_resize_split(_vq, num);
>>
>> -       return virtqueue_enable_after_reset(_vq);
>> +       err_reset = virtqueue_enable_after_reset(_vq);
> 
> I wonder if we should call virtqueue_enable_after_reset() when
> virtqueue_resize_xxx() fail.

Original code modified by ad48d53b5b3f did the reset. And the commit removes it without 
explanation.

And as we did a virtqueue_disable_and_recycle(), I think we need the 
virtqueue_enable_after_reset() to restart the queue.

In virtnet_tx_resize(), we have virtnet_tx_resume() unconditionnaly, even in case of error 
of virtqueue_resize(). virtnet_tx_resize() is called by virtnet_set_ringparam(), that is 
the function called by 'ethtool -G' and I think a failure of ethtool should not break the 
virtqueue.

Thanks,
Laurent


> 
> Thanks
> 
>> +       if (err_reset)
>> +               return err_reset;
>> +
>> +       return err;
>>   }
>>   EXPORT_SYMBOL_GPL(virtqueue_resize);
>>
>> --
>> 2.49.0
>>
>