drm/amdkfd: fix double free mem structure

drm_gem_object_put calls release_notify callback to free the mem
structure and unreserve_mem_limit, move it down after the last access
of mem and make it conditional call.
Signed-off-by: Philip Yang <Philip.Yang@amd.com>
Reviewed-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

@@ -1460,7 +1460,7 @@ int amdgpu_amdkfd_gpuvm_alloc_memory_of_gpu(
 	struct sg_table *sg = NULL;
 	uint64_t user_addr = 0;
 	struct amdgpu_bo *bo;
-	struct drm_gem_object *gobj;
+	struct drm_gem_object *gobj = NULL;
 	u32 domain, alloc_domain;
 	u64 alloc_flags;
 	int ret;
@@ -1582,14 +1582,16 @@ int amdgpu_amdkfd_gpuvm_alloc_memory_of_gpu(
 err_pin_bo:
 	drm_vma_node_revoke(&gobj->vma_node, drm_priv);
 err_node_allow:
-	drm_gem_object_put(gobj);
 	/* Don't unreserve system mem limit twice */
 	goto err_reserve_limit;
 err_bo_create:
 	unreserve_mem_limit(adev, size, flags);
 err_reserve_limit:
 	mutex_destroy(&(*mem)->lock);
-	kfree(*mem);
+	if (gobj)
+		drm_gem_object_put(gobj);
+	else
+		kfree(*mem);
 err:
 	if (sg) {
 		sg_free_table(sg);