[PATCH v2] vhost: add new `rte_vhost_vring_call_nonblock` API

[Maxime Coquelin]

Hi Changpeng,

On 10/12/22 08:40, Changpeng Liu wrote:
> Vhost-user library locks all VQ's access lock when processing
> vring based messages, such as SET_VRING_KICK and SET_VRING_CALL,
> and the data processing thread may already be started, e.g: SPDK
> vhost-blk and vhost-scsi will start the data processing thread
> when one vring is ready, then deadlock may happen when SPDK is
> posting interrupts to VM.  Here, we add a new API which allows
> caller to try again later for this case.
> 
> Bugzilla ID: 1015
> Fixes: c5736998305d ("vhost: fix missing virtqueue lock protection")
> 
> Signed-off-by: Changpeng Liu <changpeng.liu at intel.com>
> ---
>   lib/vhost/rte_vhost.h | 15 +++++++++++++++
>   lib/vhost/version.map |  3 +++
>   lib/vhost/vhost.c     | 30 ++++++++++++++++++++++++++++++
>   3 files changed, 48 insertions(+)
> 
> diff --git a/lib/vhost/rte_vhost.h b/lib/vhost/rte_vhost.h
> index bb7d86a432..d22b25cd4e 100644
> --- a/lib/vhost/rte_vhost.h
> +++ b/lib/vhost/rte_vhost.h
> @@ -909,6 +909,21 @@ rte_vhost_clr_inflight_desc_packed(int vid, uint16_t vring_idx,
>    */
>   int rte_vhost_vring_call(int vid, uint16_t vring_idx);
>   
> +/**
> + * Notify the guest that used descriptors have been added to the vring.  This
> + * function acts as a memory barrier.  This function will return -EAGAIN when
> + * vq's access lock is held by other thread, user should try again later.
> + *
> + * @param vid
> + *  vhost device ID
> + * @param vring_idx
> + *  vring index
> + * @return
> + *  0 on success, -1 on failure, -EAGAIN for another retry
> + */
> +__rte_experimental
> +int rte_vhost_vring_call_nonblock(int vid, uint16_t vring_idx);
> +
>   /**
>    * Get vhost RX queue avail count.
>    *
> diff --git a/lib/vhost/version.map b/lib/vhost/version.map
> index 7a00b65740..c8c44b8326 100644
> --- a/lib/vhost/version.map
> +++ b/lib/vhost/version.map
> @@ -94,6 +94,9 @@ EXPERIMENTAL {
>   	rte_vhost_async_try_dequeue_burst;
>   	rte_vhost_driver_get_vdpa_dev_type;
>   	rte_vhost_clear_queue;
> +
> +	# added in 22.11
> +	rte_vhost_vring_call_nonblock;
>   };
>   
>   INTERNAL {
> diff --git a/lib/vhost/vhost.c b/lib/vhost/vhost.c
> index 8740aa2788..ed6efb003f 100644
> --- a/lib/vhost/vhost.c
> +++ b/lib/vhost/vhost.c
> @@ -1317,6 +1317,36 @@ rte_vhost_vring_call(int vid, uint16_t vring_idx)
>   	return 0;
>   }
>   
> +int
> +rte_vhost_vring_call_nonblock(int vid, uint16_t vring_idx)
> +{
> +	struct virtio_net *dev;
> +	struct vhost_virtqueue *vq;
> +
> +	dev = get_device(vid);
> +	if (!dev)
> +		return -1;
> +
> +	if (vring_idx >= VHOST_MAX_VRING)
> +		return -1;
> +
> +	vq = dev->virtqueue[vring_idx];
> +	if (!vq)
> +		return -1;
> +
> +	if (!rte_spinlock_trylock(&vq->access_lock))
> +		return -EAGAIN;
> +
> +	if (vq_is_packed(dev))
> +		vhost_vring_call_packed(dev, vq);
> +	else
> +		vhost_vring_call_split(dev, vq);
> +
> +	rte_spinlock_unlock(&vq->access_lock);
> +
> +	return 0;
> +}
> +
>   uint16_t
>   rte_vhost_avail_entries(int vid, uint16_t queue_id)
>   {

Reviewed-by: Maxime Coquelin <maxime.coquelin at redhat.com>

Thanks,
Maxime