[dpdk-stable] [PATCH v2] vhost: fix vid allocation race

[Peng He]

vhost_new_device might be called in different threads at the same time.
thread 1(config thread)
            rte_vhost_driver_start
               ->vhost_user_start_client
                   ->vhost_user_add_connection
                     -> vhost_new_device

thread 2(vhost-events)
	vhost_user_read_cb
           ->vhost_user_msg_handler (return value < 0)
             -> vhost_user_start_client
                 -> vhost_new_device

So there could be a case that a same vid has been allocated twice, or
some vid might be lost in DPDK lib however still held by the upper
applications.

Another place where race would happen is at the func *vhost_destroy_device*,
but after a detailed investigation, the race does not exist as long as
no two devices have the same vid: Calling vhost_destroy_devices in
different threads with different vids is actually safe.

Fixes: a277c715987 ("vhost: refactor code structure")
Reported-by: Peng He <hepeng.0320 at bytedance.com>
Signed-off-by: Fei Chen <chenwei.0515 at bytedance.com>
Reviewed-by: Zhihong Wang <wangzhihong.wzh at bytedance.com>
---
 lib/librte_vhost/vhost.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/lib/librte_vhost/vhost.c b/lib/librte_vhost/vhost.c
index efb136edd1..52ab93d1ec 100644
--- a/lib/librte_vhost/vhost.c
+++ b/lib/librte_vhost/vhost.c
@@ -26,6 +26,7 @@
 #include "vhost_user.h"
 
 struct virtio_net *vhost_devices[MAX_VHOST_DEVICE];
+pthread_mutex_t vhost_dev_lock = PTHREAD_MUTEX_INITIALIZER;
 
 /* Called with iotlb_lock read-locked */
 uint64_t
@@ -645,6 +646,7 @@ vhost_new_device(void)
 	struct virtio_net *dev;
 	int i;
 
+	pthread_mutex_lock(&vhost_dev_lock);
 	for (i = 0; i < MAX_VHOST_DEVICE; i++) {
 		if (vhost_devices[i] == NULL)
 			break;
@@ -653,6 +655,7 @@ vhost_new_device(void)
 	if (i == MAX_VHOST_DEVICE) {
 		VHOST_LOG_CONFIG(ERR,
 			"Failed to find a free slot for new device.\n");
+		pthread_mutex_unlock(&vhost_dev_lock);
 		return -1;
 	}
 
@@ -660,10 +663,13 @@ vhost_new_device(void)
 	if (dev == NULL) {
 		VHOST_LOG_CONFIG(ERR,
 			"Failed to allocate memory for new dev.\n");
+		pthread_mutex_unlock(&vhost_dev_lock);
 		return -1;
 	}
 
 	vhost_devices[i] = dev;
+	pthread_mutex_unlock(&vhost_dev_lock);
+
 	dev->vid = i;
 	dev->flags = VIRTIO_DEV_BUILTIN_VIRTIO_NET;
 	dev->slave_req_fd = -1;
-- 
2.23.0