[PATCH 1/1] vhost: do not reset used_memslots when destroying vhost dev

[yuanminghao]

The global used_memslots or used_shared_memslots is updated to 0 unexpectly
when a vhost device destroyed. This can occur during scenarios such as live
detaching a vhost device or restarting a vhost-user net backend (e.g., 
OVS-DPDK):
 #0  vhost_commit(listener) at hw/virtio/vhost.c:439
 #1  listener_del_address_space(as, listener) at memory.c:2777
 #2  memory_listener_unregister(listener) at memory.c:2823
 #3  vhost_dev_cleanup(hdev) at hw/virtio/vhost.c:1406
 #4  vhost_net_cleanup(net) at hw/net/vhost_net.c:402
 #5  vhost_user_start(be, ncs, queues) at net/vhost-user.c:113
 #6  net_vhost_user_event(opaque, event) at net/vhost-user.c:281
 #7  tcp_chr_new_client(chr, sioc) at chardev/char-socket.c:924
 #8  tcp_chr_accept(listener, cioc, opaque) at chardev/char-socket.c:961

So we skip the update of used_memslots and used_shared_memslots when destroying
vhost devices, and it should work event if all vhost devices are removed.

Signed-off-by: yuanminghao <yuanm...@chinatelecom.cn>
---
 hw/virtio/vhost.c         | 14 +++++++++-----
 include/hw/virtio/vhost.h |  1 +
 2 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index 6aa72fd434..2258a12066 100644
--- a/hw/virtio/vhost.c
+++ b/hw/virtio/vhost.c
@@ -666,11 +666,13 @@ static void vhost_commit(MemoryListener *listener)
     dev->mem = g_realloc(dev->mem, regions_size);
     dev->mem->nregions = dev->n_mem_sections;
 
-    if (dev->vhost_ops->vhost_backend_no_private_memslots &&
-        dev->vhost_ops->vhost_backend_no_private_memslots(dev)) {
-        used_shared_memslots = dev->mem->nregions;
-    } else {
-        used_memslots = dev->mem->nregions;
+    if (!dev->listener_removing) {
+        if (dev->vhost_ops->vhost_backend_no_private_memslots &&
+            dev->vhost_ops->vhost_backend_no_private_memslots(dev)) {
+            used_shared_memslots = dev->mem->nregions;
+        } else {
+            used_memslots = dev->mem->nregions;
+        }
     }
 
     for (i = 0; i < dev->n_mem_sections; i++) {
@@ -1668,7 +1670,9 @@ void vhost_dev_cleanup(struct vhost_dev *hdev)
     }
     if (hdev->mem) {
         /* those are only safe after successful init */
+        hdev->listener_removing = true;
         memory_listener_unregister(&hdev->memory_listener);
+        hdev->listener_removing = false;
         QLIST_REMOVE(hdev, entry);
     }
     migrate_del_blocker(&hdev->migration_blocker);
diff --git a/include/hw/virtio/vhost.h b/include/hw/virtio/vhost.h
index a9469d50bc..037f85b642 100644
--- a/include/hw/virtio/vhost.h
+++ b/include/hw/virtio/vhost.h
@@ -133,6 +133,7 @@ struct vhost_dev {
     QLIST_HEAD(, vhost_iommu) iommu_list;
     IOMMUNotifier n;
     const VhostDevConfigOps *config_ops;
+    bool listener_removing;
 };
 
 extern const VhostOps kernel_ops;
-- 
2.27.0