drm/ttm: fix deref of bo->ttm without holding the lock v2

We need to grab the resv lock first before doing that check.

v2 (chk): simplify the change for -fixes
Signed-off-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Huang Rui <ray.huang@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210528130041.1683-1-christian.koenig@amd.com

drivers/gpu/drm/ttm/ttm_bo.c

@@ -1172,7 +1172,10 @@ int ttm_bo_swapout(struct ttm_buffer_object *bo, struct ttm_operation_ctx *ctx,
 	if (!ttm_bo_evict_swapout_allowable(bo, ctx, &locked, NULL))
 		return -EBUSY;
 
-	if (!ttm_bo_get_unless_zero(bo)) {
+	if (!bo->ttm || !ttm_tt_is_populated(bo->ttm) ||
+	    bo->ttm->page_flags & TTM_PAGE_FLAG_SG ||
+	    bo->ttm->page_flags & TTM_PAGE_FLAG_SWAPPED ||
+	    !ttm_bo_get_unless_zero(bo)) {
 		if (locked)
 			dma_resv_unlock(bo->base.resv);
 		return -EBUSY;

drivers/gpu/drm/ttm/ttm_device.c

@@ -143,14 +143,8 @@ int ttm_device_swapout(struct ttm_device *bdev, struct ttm_operation_ctx *ctx,
 
 		for (j = 0; j < TTM_MAX_BO_PRIORITY; ++j) {
 			list_for_each_entry(bo, &man->lru[j], lru) {
-				uint32_t num_pages;
+				uint32_t num_pages = PFN_UP(bo->base.size);
 
-				if (!bo->ttm || !ttm_tt_is_populated(bo->ttm) ||
-				    bo->ttm->page_flags & TTM_PAGE_FLAG_SG ||
-				    bo->ttm->page_flags & TTM_PAGE_FLAG_SWAPPED)
-					continue;
-
-				num_pages = bo->ttm->num_pages;
 				ret = ttm_bo_swapout(bo, ctx, gfp_flags);
 				/* ttm_bo_swapout has dropped the lru_lock */
 				if (!ret)