drm/prime: add exported buffers to current fprivs imported buffer list (v2)

If userspace attempts to import a buffer it exported on the same device,
we need to return the same GEM handle for it, not a new handle pointing
at the same GEM object.

v2: move removals into a single fn, no need to set to NULL. (Chris Wilson)
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_gem.c

@@ -201,6 +201,19 @@ drm_gem_object_alloc(struct drm_device *dev, size_t size)
 }
 EXPORT_SYMBOL(drm_gem_object_alloc);
 
+static void
+drm_gem_remove_prime_handles(struct drm_gem_object *obj, struct drm_file *filp)
+{
+	if (obj->import_attach) {
+		drm_prime_remove_imported_buf_handle(&filp->prime,
+				obj->import_attach->dmabuf);
+	}
+	if (obj->export_dma_buf) {
+		drm_prime_remove_imported_buf_handle(&filp->prime,
+				obj->export_dma_buf);
+	}
+}
+
 /**
  * Removes the mapping from handle to filp for this object.
  */
@@ -233,9 +246,7 @@ drm_gem_handle_delete(struct drm_file *filp, u32 handle)
 	idr_remove(&filp->object_idr, handle);
 	spin_unlock(&filp->table_lock);
 
-	if (obj->import_attach)
-		drm_prime_remove_imported_buf_handle(&filp->prime,
-				obj->import_attach->dmabuf);
+	drm_gem_remove_prime_handles(obj, filp);
 
 	if (dev->driver->gem_close_object)
 		dev->driver->gem_close_object(obj, filp);
@@ -530,9 +541,7 @@ drm_gem_object_release_handle(int id, void *ptr, void *data)
 	struct drm_gem_object *obj = ptr;
 	struct drm_device *dev = obj->dev;
 
-	if (obj->import_attach)
-		drm_prime_remove_imported_buf_handle(&file_priv->prime,
-				obj->import_attach->dmabuf);
+	drm_gem_remove_prime_handles(obj, file_priv);
 
 	if (dev->driver->gem_close_object)
 		dev->driver->gem_close_object(obj, file_priv);

drivers/gpu/drm/drm_prime.c

@@ -68,6 +68,7 @@ int drm_gem_prime_handle_to_fd(struct drm_device *dev,
 {
 	struct drm_gem_object *obj;
 	void *buf;
+	int ret;
 
 	obj = drm_gem_object_lookup(dev, file_priv, handle);
 	if (!obj)
@@ -100,6 +101,17 @@ int drm_gem_prime_handle_to_fd(struct drm_device *dev,
 		obj->export_dma_buf = buf;
 		*prime_fd = dma_buf_fd(buf, flags);
 	}
+	/* if we've exported this buffer the cheat and add it to the import list
+	 * so we get the correct handle back
+	 */
+	ret = drm_prime_add_imported_buf_handle(&file_priv->prime,
+			obj->export_dma_buf, handle);
+	if (ret) {
+		drm_gem_object_unreference_unlocked(obj);
+		mutex_unlock(&file_priv->prime.lock);
+		return ret;
+	}
+
 	mutex_unlock(&file_priv->prime.lock);
 	return 0;
 }