Re: [PATCH V2 5/6] vhost_net: poll vhost queue after marking DMA is done

Jason Wang
2013-09-02T03:06:54Z

On 08/31/2013 12:44 AM, Ben Hutchings wrote:
> On Fri, 2013-08-30 at 12:29 +0800, Jason Wang wrote:
>> We used to poll vhost queue before making DMA is done, this is racy if vhost
>> thread were waked up before marking DMA is done which can result the signal to
>> be missed. Fix this by always poll the vhost thread before DMA is done.
> Does this bug only exist in net-next or is it older? Should the fix go
> to net and stable branches?

This should go for the stable branches too (3.4 above).

Thanks for the checking.
>
> Ben.
>
>> Signed-off-by: Jason Wang <jasowang@redhat.com>
>> ---
>> drivers/vhost/net.c | 9 +++++----
>> 1 files changed, 5 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
>> index ff60c2a..d09c17c 100644
>> --- a/drivers/vhost/net.c
>> +++ b/drivers/vhost/net.c
>> @@ -308,6 +308,11 @@ static void vhost_zerocopy_callback(struct ubuf_info *ubuf, bool success)
>> struct vhost_virtqueue *vq = ubufs->vq;
>> int cnt = atomic_read(&ubufs->kref.refcount);
>>
>> + /* set len to mark this desc buffers done DMA */
>> + vq->heads[ubuf->desc].len = success ?
>> + VHOST_DMA_DONE_LEN : VHOST_DMA_FAILED_LEN;
>> + vhost_net_ubuf_put(ubufs);
>> +
>> /*
>> * Trigger polling thread if guest stopped submitting new buffers:
>> * in this case, the refcount after decrement will eventually reach 1
>> @@ -318,10 +323,6 @@ static void vhost_zerocopy_callback(struct ubuf_info *ubuf, bool success)
>> */
>> if (cnt <= 2 || !(cnt % 16))
>> vhost_poll_queue(&vq->poll);
>> - /* set len to mark this desc buffers done DMA */
>> - vq->heads[ubuf->desc].len = success ?
>> - VHOST_DMA_DONE_LEN : VHOST_DMA_FAILED_LEN;
>> - vhost_net_ubuf_put(ubufs);
>> }
>>
>> /* Expects to be always run from workqueue - which acts as