[dpdk-dev] [PATCH v2 4/4] vhost: fix async register/unregister deadlock

[Patrick Fu <patrick.fu@intel.com>]

When async register/unregister function is invoked in certain vhost
event callbacks (e.g. vring state change), deadlock may occur due to
recursive spinlock acquire. This patch removes unnecessary spinlock
from register API and use 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      | 13 +++++++------
 lib/librte_vhost/vhost_user.c |  4 ++--
 2 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/lib/librte_vhost/vhost.c b/lib/librte_vhost/vhost.c
index 919a5bf7f..c247fc900 100644
--- a/lib/librte_vhost/vhost.c
+++ b/lib/librte_vhost/vhost.c
@@ -1577,8 +1577,6 @@ int rte_vhost_async_channel_register(int vid, uint16_t queue_id,
 		ops->transfer_data == NULL))
 		return -1;
 
-	rte_spinlock_lock(&vq->access_lock);
-
 	if (unlikely(vq->async_registered)) {
 		VHOST_LOG_CONFIG(ERR,
 			"async register failed: channel already registered "
@@ -1623,8 +1621,6 @@ int rte_vhost_async_channel_register(int vid, uint16_t queue_id,
 	vq->async_registered = true;
 
 reg_out:
-	rte_spinlock_unlock(&vq->access_lock);
-
 	return 0;
 }
 
@@ -1643,10 +1639,15 @@ 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 67d2a2d43..c8d74bde6 100644
--- a/lib/librte_vhost/vhost_user.c
+++ b/lib/librte_vhost/vhost_user.c
@@ -2043,9 +2043,9 @@ 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;
 		}
-- 
2.18.4