drm/udl: Don't call get/put_pages on imported dma-buf

There's no direct harm, because for the shmem helpers these are noops
on imported buffers. The trouble is in the locks these take - I want
to change dma_buf_vmap locking, and so need to make sure that we only
ever take certain locks on one side of the dma-buf interface: Either
for exporters, or for importers.
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Dave Airlie <airlied@redhat.com>
Cc: Sean Paul <sean@poorly.run>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200511093554.211493-6-daniel.vetter@ffwll.ch

drivers/gpu/drm/udl/udl_gem.c

@@ -46,29 +46,31 @@ static void *udl_gem_object_vmap(struct drm_gem_object *obj)
 	if (shmem->vmap_use_count++ > 0)
 		goto out;
 
-	ret = drm_gem_shmem_get_pages(shmem);
-	if (ret)
-		goto err_zero_use;
-
-	if (obj->import_attach)
+	if (obj->import_attach) {
 		shmem->vaddr = dma_buf_vmap(obj->import_attach->dmabuf);
-	else
+	} else {
+		ret = drm_gem_shmem_get_pages(shmem);
+		if (ret)
+			goto err;
+
 		shmem->vaddr = vmap(shmem->pages, obj->size >> PAGE_SHIFT,
 				    VM_MAP, PAGE_KERNEL);
 
+		if (!shmem->vaddr)
+			drm_gem_shmem_put_pages(shmem);
+	}
+
 	if (!shmem->vaddr) {
 		DRM_DEBUG_KMS("Failed to vmap pages\n");
 		ret = -ENOMEM;
-		goto err_put_pages;
+		goto err;
 	}
 
 out:
 	mutex_unlock(&shmem->vmap_lock);
 	return shmem->vaddr;
 
-err_put_pages:
-	drm_gem_shmem_put_pages(shmem);
-err_zero_use:
+err:
 	shmem->vmap_use_count = 0;
 	mutex_unlock(&shmem->vmap_lock);
 	return ERR_PTR(ret);