On Mon, 2024-12-09 at 19:08 +0100, Michal Hocko wrote: > On Mon 09-12-24 12:42:33, Rik van Riel wrote: > > It is possible for programs to get stuck in exit, when their > > memcg is at or above the memory.max limit, and things like > > the do_futex() call from mm_release() need to page memory in. > > > > This can hang forever, but it really doesn't have to. > > Are you sure this is really happening? It turns out it wasn't really forever. After about a day the zombie task I was bpftracing, to figure out exactly what was going wrong, finally succeeded in exiting. I got as far as seeing try_to_free_mem_cgroup_pages return 0 many, times in a row, looping in try_charge_memcg, which occasionally returned -ENOMEM to the caller, who then retried several times. Each invocation of try_to_free_mem_cgroup_pages also saw a large number of unsuccessful calls to shrink_folio_list. It looks like what might be happening instead is that faultin_page() returns 0 after getting back VM_FAULT_OOM from handle_mm_fault, causing __get_user_pages() to loop. Let me send a patch to fix that, instead! -- All Rights Reversed.
