On Tue 14-01-25 11:09:55, Johannes Weiner wrote: > Hi, > > On Mon, Dec 16, 2024 at 04:39:12PM +0100, Michal Hocko wrote: > > On Thu 12-12-24 13:30:12, Johannes Weiner wrote: [...] > > > If we return -ENOMEM to an OOM victim in a fault, the fault handler > > > will re-trigger OOM, which will find the existing OOM victim and do > > > nothing, then restart the fault. > > > > IIRC the task will handle the pending SIGKILL if the #PF fails. If the > > charge happens from the exit path then we rely on ENOMEM returned from > > gup as a signal to back off. Do we have any caller that keeps retrying > > on ENOMEM? > > 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. > 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? -- Michal Hocko SUSE Labs
