On Tue, 2025-01-14 at 17:46 +0100, Michal Hocko wrote: > On Tue 14-01-25 11:09:55, Johannes Weiner wrote: > > > > > We managed to extract a stack trace of the livelocked task: > > > > obj_cgroup_may_swap > > zswap_store > > swap_writepage > > shrink_folio_list > > shrink_lruvec > > shrink_node > > do_try_to_free_pages > > try_to_free_mem_cgroup_pages > > OK, so this is the reclaim path and it fails due to reasons you > mention > below. This will retry several times until it hits mem_cgroup_oom > which > will bail in mem_cgroup_out_of_memory because of task_is_dying > (returns > true) and retry the charge + reclaim (as the oom killer hasn't done > anything) with passed_oom = true this time and eventually got to > nomem > path and returns ENOMEM. This should propaged -ENOMEM down the path > > > charge_memcg > > mem_cgroup_swapin_charge_folio > > __read_swap_cache_async > > swapin_readahead > > do_swap_page > > handle_mm_fault > > do_user_addr_fault > > exc_page_fault > > asm_exc_page_fault > > __get_user > > All the way here and return the failure to futex_cleanup which > doesn't > retry __get_user on the failure AFAICS (exit_robust_list). But I > might > be missing something, it's been quite some time since I've looked > into > futex code. Can you explain how -ENOMEM would get propagated down past the page fault handler? This isn't get_user_pages(), which can just pass -ENOMEM on to the caller. If there is code to pass -ENOMEM on past the page fault exception handler, I have not been able to find it. How does this work? > > > futex_cleanup > > fuxtex_exit_release > > do_exit > > do_group_exit > > get_signal > > arch_do_signal_or_restart > > exit_to_user_mode_prepare > > syscall_exit_to_user_mode > > do_syscall > > entry_SYSCALL_64 > > syscall > > > > Both memory.max and memory.zswap.max are hit. I don't see how this > > could ever make forward progress - the futex fault will retry until > > it > > succeeds. > > I must be missing something but I do not see the retry, could you > point > me where this is happening please? > -- All Rights Reversed.
