drm/vmwgfx: Fix regression caused by "drm/ttm: make ttm reservation calls behave like reservation calls"

The call to ttm_eu_backoff_reservation() as part of an error path would cause
a lock imbalance if the reservation ticket was not initialized. This error is
easily triggered from user-space by submitting a bogus command stream.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Jakob Bornecrantz <jakob@vmware.com>
Cc: stable@vger.kernel.org
Cc: Maarten Lankhorst <maarten.lankhorst@canonical.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c

@@ -2195,11 +2195,11 @@ int vmw_execbuf_process(struct drm_file *file_priv,
 	ret = vmw_cmd_check_all(dev_priv, sw_context, kernel_commands,
 				command_size);
 	if (unlikely(ret != 0))
-		goto out_err;
+		goto out_err_nores;
 
 	ret = vmw_resources_reserve(sw_context);
 	if (unlikely(ret != 0))
-		goto out_err;
+		goto out_err_nores;
 
 	ret = ttm_eu_reserve_buffers(&ticket, &sw_context->validate_nodes);
 	if (unlikely(ret != 0))
@@ -2291,10 +2291,11 @@ int vmw_execbuf_process(struct drm_file *file_priv,
 out_unlock_binding:
 	mutex_unlock(&dev_priv->binding_mutex);
 out_err:
+	ttm_eu_backoff_reservation(&ticket, &sw_context->validate_nodes);
+out_err_nores:
+	vmw_resource_list_unreserve(&sw_context->resource_list, true);
 	vmw_resource_relocations_free(&sw_context->res_relocations);
 	vmw_free_relocations(sw_context);
-	ttm_eu_backoff_reservation(&ticket, &sw_context->validate_nodes);
-	vmw_resource_list_unreserve(&sw_context->resource_list, true);
 	vmw_clear_validations(sw_context);
 	if (unlikely(dev_priv->pinned_bo != NULL &&
 		     !dev_priv->query_cid_valid))