struct usb_device *udev;
        struct drm_crtc *crtc;
 
+       /* active framebuffer on the 16-bit channel */
+       const struct drm_framebuffer *active_fb_16;
+       spinlock_t active_fb_16_lock;
+
        struct mutex gem_lock;
 
        int sku_pixel_limit;
 struct udl_framebuffer {
        struct drm_framebuffer base;
        struct drm_gem_shmem_object *shmem;
-       bool active_16; /* active on the 16-bit channel */
 };
 
 #define to_udl_fb(x) container_of(x, struct udl_framebuffer, base)
 
        BUG_ON(!is_power_of_2(fb->base.format->cpp[0]));
        log_bpp = __ffs(fb->base.format->cpp[0]);
 
-       if (!fb->active_16)
+       spin_lock(&udl->active_fb_16_lock);
+       if (udl->active_fb_16 != &fb->base) {
+               spin_unlock(&udl->active_fb_16_lock);
                return 0;
+       }
+       spin_unlock(&udl->active_fb_16_lock);
 
        vaddr = drm_gem_shmem_vmap(&fb->shmem->base);
        if (IS_ERR(vaddr)) {
                                      unsigned num_clips)
 {
        struct udl_framebuffer *ufb = to_udl_fb(fb);
+       struct udl_device *udl = fb->dev->dev_private;
        struct dma_buf_attachment *import_attach;
        int i;
        int ret = 0;
 
        drm_modeset_lock_all(fb->dev);
 
-       if (!ufb->active_16)
+       spin_lock(&udl->active_fb_16_lock);
+       if (udl->active_fb_16 != fb) {
+               spin_unlock(&udl->active_fb_16_lock);
                goto unlock;
+       }
+       spin_unlock(&udl->active_fb_16_lock);
 
        import_attach = ufb->shmem->base.import_attach;
 
 
 
        DRM_DEBUG("\n");
 
+       udl->active_fb_16 = NULL;
+       spin_lock_init(&udl->active_fb_16_lock);
+
        mutex_init(&udl->gem_lock);
 
        if (!udl_parse_vendor_descriptor(dev, udl->udev)) {
 
 
        wrptr = udl_dummy_render(wrptr);
 
-       if (old_fb) {
-               struct udl_framebuffer *uold_fb = to_udl_fb(old_fb);
-               uold_fb->active_16 = false;
-       }
-       ufb->active_16 = true;
+       spin_lock(&udl->active_fb_16_lock);
+       udl->active_fb_16 = &ufb->base;
+       spin_unlock(&udl->active_fb_16_lock);
        udl->mode_buf_len = wrptr - buf;
 
        /* damage all of it */
 {
        struct udl_framebuffer *ufb = to_udl_fb(fb);
        struct drm_device *dev = crtc->dev;
+       struct udl_device *udl = dev->dev_private;
 
-       struct drm_framebuffer *old_fb = crtc->primary->fb;
-       if (old_fb) {
-               struct udl_framebuffer *uold_fb = to_udl_fb(old_fb);
-               uold_fb->active_16 = false;
-       }
-       ufb->active_16 = true;
+       spin_lock(&udl->active_fb_16_lock);
+       udl->active_fb_16 = fb;
+       spin_unlock(&udl->active_fb_16_lock);
 
        udl_handle_damage(ufb, 0, 0, fb->width, fb->height);