There is a WARNING in kmem_cache_destroy() for the cases when a cache is destroyed with live objects: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/mm/slab_common.c?id=e0dccc3b76fb35bb257b4118367a883073d7390e#n506 When KASAN is enabled we could print allocation stacks for all leaked objects to give more useful info for debugging. For context see: https://lore.kernel.org/all/2916828.W3qMjvkFlE@silver/
Allocation stacks may always be the same for custom caches, but they may also be different. E.g. in this case the allocation happens in a common p9_client_prepare_req() function that it called in multiple places. But KASAN can also provide "aux" stacks that may also give some glues.