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

Ben Hutchings
2013-08-30T16:44:33Z

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?

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

--
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.