drm/ttm: fix fence locking in ttm_buffer_object_transfer, 2nd try

danvet · airlied · commit ff7c60c580d9 · 2013-02-08T10:44:31.000+10:00
This fixes up commit e8e8962 Author: Daniel Vetter <daniel.vetter@ffwll.ch> Date: Tue Dec 18 22:25:11 2012 +0100 drm/ttm: fix fence locking in ttm_buffer_object_transfer which leaves behind a might_sleep in atomic context, since the fence_lock spinlock is held over a kmalloc(GFP_KERNEL) call. The fix is to revert the above commit and only take the lock where we need it, around the call to ->sync_obj_ref. v2: Fixup things noticed by Maarten Lankhorst: - Brown paper bag locking bug. - No need for kzalloc if we clear the entire thing on the next line. - check for bo->sync_obj (totally unlikely race, but still someone else could have snuck in) and clear fbo->sync_obj if it's cleared already. Reported-by: Dave Airlie <airlied@gmail.com> Cc: Jerome Glisse <jglisse@redhat.com> Cc: Maarten Lankhorst <maarten.lankhorst@canonical.com> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch> Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/drivers/gpu/drm/ttm/ttm_bo_util.c b/drivers/gpu/drm/ttm/ttm_bo_util.c
@@ -429,7 +429,7 @@ static int ttm_buffer_object_transfer(struct ttm_buffer_object *bo,
 	struct ttm_bo_device *bdev = bo->bdev;
 	struct ttm_bo_driver *driver = bdev->driver;
 
-	fbo = kzalloc(sizeof(*fbo), GFP_KERNEL);
+	fbo = kmalloc(sizeof(*fbo), GFP_KERNEL);
 	if (!fbo)
 		return -ENOMEM;
 
@@ -448,7 +448,12 @@ static int ttm_buffer_object_transfer(struct ttm_buffer_object *bo,
 	fbo->vm_node = NULL;
 	atomic_set(&fbo->cpu_writers, 0);
 
-	fbo->sync_obj = driver->sync_obj_ref(bo->sync_obj);
+	spin_lock(&bdev->fence_lock);
+	if (bo->sync_obj)
+		fbo->sync_obj = driver->sync_obj_ref(bo->sync_obj);
+	else
+		fbo->sync_obj = NULL;
+	spin_unlock(&bdev->fence_lock);
 	kref_init(&fbo->list_kref);
 	kref_init(&fbo->kref);
 	fbo->destroy = &ttm_transfered_destroy;
@@ -661,13 +666,11 @@ int ttm_bo_move_accel_cleanup(struct ttm_buffer_object *bo,
 		 */
 
 		set_bit(TTM_BO_PRIV_FLAG_MOVING, &bo->priv_flags);
-
-		/* ttm_buffer_object_transfer accesses bo->sync_obj */
-		ret = ttm_buffer_object_transfer(bo, &ghost_obj);
 		spin_unlock(&bdev->fence_lock);
 		if (tmp_obj)
 			driver->sync_obj_unref(&tmp_obj);
 
+		ret = ttm_buffer_object_transfer(bo, &ghost_obj);
 		if (ret)
 			return ret;
 
