[v4,4/4] vhost: fix async unregister deadlock

  When async unregister function is invoked in certain vhost event
callbacks (e.g. vring state change), deadlock may occur due to
recursive spinlock acquire. This patch uses trylock() primitive in
the unregister API to avoid deadlock.

Fixes: 78639d54563a ("vhost: introduce async enqueue registration API")

Signed-off-by: Patrick Fu <patrick.fu@intel.com>
---
 lib/librte_vhost/vhost.c      | 9 +++++++--
 lib/librte_vhost/vhost_user.c | 4 ++--
 2 files changed, 9 insertions(+), 4 deletions(-)
  

On 10/13/20 3:45 AM, Patrick Fu wrote:
> When async unregister function is invoked in certain vhost event
> callbacks (e.g. vring state change), deadlock may occur due to
> recursive spinlock acquire. This patch uses trylock() primitive in
> the unregister API to avoid deadlock.
> 
> Fixes: 78639d54563a ("vhost: introduce async enqueue registration API")
> 
> Signed-off-by: Patrick Fu <patrick.fu@intel.com>
> ---
>  lib/librte_vhost/vhost.c      | 9 +++++++--
>  lib/librte_vhost/vhost_user.c | 4 ++--
>  2 files changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/lib/librte_vhost/vhost.c b/lib/librte_vhost/vhost.c
> index 323565898..6068c38ec 100644
> --- a/lib/librte_vhost/vhost.c
> +++ b/lib/librte_vhost/vhost.c
> @@ -1633,10 +1633,15 @@ int rte_vhost_async_channel_unregister(int vid, uint16_t queue_id)
>  		return ret;
>  
>  	ret = 0;
> -	rte_spinlock_lock(&vq->access_lock);
>  
>  	if (!vq->async_registered)
> -		goto out;
> +		return ret;
> +
> +	if (!rte_spinlock_trylock(&vq->access_lock)) {
> +		VHOST_LOG_CONFIG(ERR, "Failed to unregister async channel. "
> +			"virt queue busy.\n");
> +		return -1;
> +	}
>  
>  	if (vq->async_pkts_inflight_n) {
>  		VHOST_LOG_CONFIG(ERR, "Failed to unregister async channel. "
> diff --git a/lib/librte_vhost/vhost_user.c b/lib/librte_vhost/vhost_user.c
> index 1656ec736..d20c8c57a 100644
> --- a/lib/librte_vhost/vhost_user.c
> +++ b/lib/librte_vhost/vhost_user.c
> @@ -1980,9 +1980,9 @@ vhost_user_set_vring_enable(struct virtio_net **pdev,
>  		"set queue enable: %d to qp idx: %d\n",
>  		enable, index);
>  
> -	if (!enable && dev->virtqueue[index]->async_registered) {
> +	if (enable && dev->virtqueue[index]->async_registered) {
>  		if (dev->virtqueue[index]->async_pkts_inflight_n) {
> -			VHOST_LOG_CONFIG(ERR, "failed to disable vring. "
> +			VHOST_LOG_CONFIG(ERR, "failed to enable vring. "
>  			"async inflight packets must be completed first\n");
>  			return RTE_VHOST_MSG_RESULT_ERR;
>  		}
> 

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

Thanks,
Maxime