[RFC PATCH 3/5] vhost: fix async access

[David Marchand <david.marchand@redhat.com>]

vq->async is protected with vq->access_lock.

Fixes: eb666d24085f ("vhost: fix async unregister deadlock")
Fixes: 0c0935c5f794 ("vhost: allow to check in-flight packets for async vhost")
Cc: stable@dpdk.org

Signed-off-by: David Marchand <david.marchand@redhat.com>
---
This has been reported by Jiayu too:
https://patchwork.dpdk.org/project/dpdk/patch/20220328020754.1155063-1-jiayu.hu@intel.com/

---
 lib/vhost/vhost.c | 25 ++++++++++---------------
 1 file changed, 10 insertions(+), 15 deletions(-)

diff --git a/lib/vhost/vhost.c b/lib/vhost/vhost.c
index 863cd9131e..9e6ca506ff 100644
--- a/lib/vhost/vhost.c
+++ b/lib/vhost/vhost.c
@@ -1753,27 +1753,23 @@ rte_vhost_async_channel_unregister(int vid, uint16_t queue_id)
 	if (vq == NULL)
 		return ret;
 
-	ret = 0;
-
-	if (!vq->async)
-		return ret;
-
 	if (vhost_spinlock_trylock(&vq->access_lock) == 0) {
 		VHOST_LOG_CONFIG(ERR, "(%s) failed to unregister async channel, virtqueue busy.\n",
 				dev->ifname);
-		return -1;
+		return ret;
 	}
 
-	if (vq->async->pkts_inflight_n) {
+	if (!vq->async) {
+		ret = 0;
+	} else if (vq->async->pkts_inflight_n) {
 		VHOST_LOG_CONFIG(ERR, "(%s) failed to unregister async channel.\n", dev->ifname);
 		VHOST_LOG_CONFIG(ERR, "(%s) inflight packets must be completed before unregistration.\n",
 			dev->ifname);
-		ret = -1;
-		goto out;
+	} else {
+		vhost_free_async_mem(vq);
+		ret = 0;
 	}
 
-	vhost_free_async_mem(vq);
-out:
 	vhost_spinlock_unlock(&vq->access_lock);
 
 	return ret;
@@ -1891,9 +1887,6 @@ rte_vhost_async_get_inflight(int vid, uint16_t queue_id)
 	if (vq == NULL)
 		return ret;
 
-	if (!vq->async)
-		return ret;
-
 	if (vhost_spinlock_trylock(&vq->access_lock) == 0) {
 		VHOST_LOG_CONFIG(DEBUG,
 			"(%s) failed to check in-flight packets. virtqueue busy.\n",
@@ -1901,7 +1894,9 @@ rte_vhost_async_get_inflight(int vid, uint16_t queue_id)
 		return ret;
 	}
 
-	ret = vq->async->pkts_inflight_n;
+	if (vq->async)
+		ret = vq->async->pkts_inflight_n;
+
 	vhost_spinlock_unlock(&vq->access_lock);
 
 	return ret;
-- 
2.23.0