drm/amdkfd: Fix memory leak in kfd_mem_dmamap_userptr()

If the number of pages from the userptr BO differs from the SG BO then the
allocated memory for the SG table doesn't get freed before returning
-EINVAL, which may lead to a memory leak in some error paths. Fix this by
checking the number of pages before allocating memory for the SG table.

Fixes: 264fb4d3 ("drm/amdgpu: Add multi-GPU DMA mapping helpers")
Signed-off-by: Rafael Mendonca <rafaelmendsr@gmail.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c

@@ -510,13 +510,13 @@ kfd_mem_dmamap_userptr(struct kgd_mem *mem,
 	struct ttm_tt *ttm = bo->tbo.ttm;
 	int ret;
 
+	if (WARN_ON(ttm->num_pages != src_ttm->num_pages))
+		return -EINVAL;
+
 	ttm->sg = kmalloc(sizeof(*ttm->sg), GFP_KERNEL);
 	if (unlikely(!ttm->sg))
 		return -ENOMEM;
 
-	if (WARN_ON(ttm->num_pages != src_ttm->num_pages))
-		return -EINVAL;
-
 	/* Same sequence as in amdgpu_ttm_tt_pin_userptr */
 	ret = sg_alloc_table_from_pages(ttm->sg, src_ttm->pages,
 					ttm->num_pages, 0,