vhost-user: fix lost reconnect again

When the vhost-user is reconnecting to the backend, and if the vhost-user fails
at the get_features in vhost_dev_init(), then the reconnect will fail
and it will not be retriggered forever.

The reason is:
When the vhost-user fail at get_features, the vhost_dev_cleanup will be called
immediately.

vhost_dev_cleanup calls 'memset(hdev, 0, sizeof(struct vhost_dev))'.

The reconnect path is:
vhost_user_blk_event
   vhost_user_async_close(.. vhost_user_blk_disconnect ..)
     qemu_chr_fe_set_handlers <----- clear the notifier callback
       schedule vhost_user_async_close_bh

The vhost->vdev is null, so the vhost_user_blk_disconnect will not be
called, then the event fd callback will not be reinstalled.

We need to ensure that even if vhost_dev_init initialization fails, the event
handler still needs to be reinstalled when s->connected is false.

All vhost-user devices have this issue, including vhost-user-blk/scsi.

Fixes: 71e076a07d ("hw/virtio: generalise CHR_EVENT_CLOSED handling")

Signed-off-by: Li Feng <fengli@smartx.com>
Message-Id: <20240516025753.130171-3-fengli@smartx.com>
Reviewed-by: Raphael Norwitz <raphael@enfabrica.net>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/block/vhost-user-blk.c

@@ -354,7 +354,7 @@ static void vhost_user_blk_disconnect(DeviceState *dev)
     VHostUserBlk *s = VHOST_USER_BLK(vdev);
 
     if (!s->connected) {
-        return;
+        goto done;
     }
     s->connected = false;
 
@@ -362,6 +362,7 @@ static void vhost_user_blk_disconnect(DeviceState *dev)
 
     vhost_dev_cleanup(&s->dev);
 
+done:
     /* Re-instate the event handler for new connections */
     qemu_chr_fe_set_handlers(&s->chardev, NULL, NULL, vhost_user_blk_event,
                              NULL, dev, NULL, true);

hw/scsi/vhost-user-scsi.c

@@ -182,7 +182,7 @@ static void vhost_user_scsi_disconnect(DeviceState *dev)
     VirtIOSCSICommon *vs = VIRTIO_SCSI_COMMON(dev);
 
     if (!s->connected) {
-        return;
+        goto done;
     }
     s->connected = false;
 
@@ -190,6 +190,7 @@ static void vhost_user_scsi_disconnect(DeviceState *dev)
 
     vhost_dev_cleanup(&vsc->dev);
 
+done:
     /* Re-instate the event handler for new connections */
     qemu_chr_fe_set_handlers(&vs->conf.chardev, NULL, NULL,
                              vhost_user_scsi_event, NULL, dev, NULL, true);

hw/virtio/vhost-user-base.c

@@ -225,13 +225,14 @@ static void vub_disconnect(DeviceState *dev)
     VHostUserBase *vub = VHOST_USER_BASE(vdev);
 
     if (!vub->connected) {
-        return;
+        goto done;
     }
     vub->connected = false;
 
     vub_stop(vdev);
     vhost_dev_cleanup(&vub->vhost_dev);
 
+done:
     /* Re-instate the event handler for new connections */
     qemu_chr_fe_set_handlers(&vub->chardev,
                              NULL, NULL, vub_event,

hw/virtio/vhost-user.c

@@ -2781,16 +2781,8 @@ typedef struct {
 static void vhost_user_async_close_bh(void *opaque)
 {
     VhostAsyncCallback *data = opaque;
-    struct vhost_dev *vhost = data->vhost;
 
-    /*
-     * If the vhost_dev has been cleared in the meantime there is
-     * nothing left to do as some other path has completed the
-     * cleanup.
-     */
-    if (vhost->vdev) {
-        data->cb(data->dev);
-    }
+    data->cb(data->dev);
 
     g_free(data);
 }