drm/ttm: fix locking in vmap/vunmap TTM GEM helpers

I've stumbled over this while reviewing patches for DMA-buf and it looks
like we completely messed the locking up here.

In general most TTM function should only be called while holding the
appropriate BO resv lock. Without this we could break the internal
buffer object state here.

Only compile tested!
Signed-off-by: Christian König <christian.koenig@amd.com>
Fixes: 43676605 ("drm/ttm: Add vmap/vunmap to TTM and TTM GEM helpers")
Cc: stable@vger.kernel.org
Reviewed-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220715111533.467012-1-christian.koenig@amd.com

drivers/gpu/drm/drm_gem_ttm_helper.c

@@ -64,8 +64,13 @@ int drm_gem_ttm_vmap(struct drm_gem_object *gem,
 		     struct iosys_map *map)
 {
 	struct ttm_buffer_object *bo = drm_gem_ttm_of_gem(gem);
+	int ret;
+
+	dma_resv_lock(gem->resv, NULL);
+	ret = ttm_bo_vmap(bo, map);
+	dma_resv_unlock(gem->resv);
 
-	return ttm_bo_vmap(bo, map);
+	return ret;
 }
 EXPORT_SYMBOL(drm_gem_ttm_vmap);
 
@@ -82,7 +87,9 @@ void drm_gem_ttm_vunmap(struct drm_gem_object *gem,
 {
 	struct ttm_buffer_object *bo = drm_gem_ttm_of_gem(gem);
 
+	dma_resv_lock(gem->resv, NULL);
 	ttm_bo_vunmap(bo, map);
+	dma_resv_unlock(gem->resv);
 }
 EXPORT_SYMBOL(drm_gem_ttm_vunmap);