Am 27.11.23 um 13:24 schrieb Karolina Stolarek:
On 24.11.2023 16:53, Christian König wrote:
@Karolina do you of hand know a way how we could exercise this in a
TTM unit test? Basically we would need to redirect the
alloc_pages_node() symbol to an unit test internal function and let
it return an error (or something like that).
Do I understand correctly that you want to mock NULL from
alloc_pages_node() in ttm_pool_alloc_page()? I had a quick look at it,
and found a(n ugly) way to do it.
KUnit provides an API to redirect calls using
KUNIT_STATIC_STUB_REDIRECT that can be registered in the original
function and then overridden in the test. You can read more about the
mechanism in [1].
The problem is that we'd need to introduce a wrapper call for
alloc_pages_node() in TTM and expose it, so the function can be
substituted during the test. We can't directly modify
alloc_pages_node() due to cyclic dependencies caused by
kunit/static_stub.h.
For example, in ttm_pool.c, we'd have:
+struct page *ttm_alloc_pages_node(int nid, gfp_t gfp_mask,
+ unsigned int order)
+{
+ KUNIT_STATIC_STUB_REDIRECT(ttm_alloc_pages_node, nid, gfp_mask,
order);
+ return alloc_pages_node(nid, gfp_mask, order);
+}
+EXPORT_SYMBOL(ttm_alloc_pages_node);
+
/* Allocate pages of size 1 << order with the given gfp_flags */
static struct page *ttm_pool_alloc_page(struct ttm_pool *pool, gfp_t
gfp_flags,
unsigned int order)
(...)
if (!pool->use_dma_alloc) {
- p = alloc_pages_node(pool->nid, gfp_flags, order);
+ p = ttm_alloc_pages_node(pool->nid, gfp_flags, order);
if (p)
p->private = order;
return p;
And in the test we would say:
+static struct page *fake_ttm_alloc_pages_node(int nid, gfp_t gfp_mask,
+ unsigned int order)
+{
+ return NULL;
+}
+
+static void ttm_pool_alloc_failed(struct kunit *test)
+{
(...)
+ kunit_activate_static_stub(test, ttm_alloc_pages_node,
+ fake_ttm_alloc_pages_node);
+ err = ttm_pool_alloc(pool, tt, &simple_ctx);
+ kunit_deactivate_static_stub(test, ttm_alloc_pages_node);
Christian, what do you think?
Yes, that was exactly what I was looking for.
And you are right that is indeed quite a bit ugly, I was hoping more
like adding debugging hooks or something like that.
Need to look into that in more detail, thanks for the pointer.
Regards,
Christian.
All the best,
Karolina
---------------------------------------------------------
[1] -
https://lore.kernel.org/all/20230128074918.1180523-1-davidgow@xxxxxxxxxx/
