On 2018/10/10 20:35, Michal Hocko wrote: >>>> What should we do if memcg-OOM found no killable task because the allocating task >>>> was oom_score_adj == -1000 ? Flooding printk() until RCU stall watchdog fires >>>> (which seems to be caused by commit 3100dab2aa09dc6e ("mm: memcontrol: print proper >>>> OOM header when no eligible victim left") because syzbot was terminating the test >>>> upon WARN(1) removed by that commit) is not a good behavior. >>> >>> We definitely want to inform about ineligible oom victim. We might >>> consider some rate limiting for the memcg state but that is a valuable >>> information to see under normal situation (when you do not have floods >>> of these situations). >>> >> >> But if the caller cannot be noticed by SIGKILL from the OOM killer, >> allowing the caller to trigger the OOM killer again and again (until >> global OOM killer triggers) is bad. > > There is simply no other option. Well, except for failing the charge > which has been considered and refused because it could trigger > unexpected error paths and that breaking the isolation on rare cases > when of the misconfiguration is acceptable. We can reconsider that > but you should bring really good arguments on the table. I was very > successful doing that. > By the way, how do we avoid this flooding? Something like this? include/linux/sched.h | 1 + mm/oom_kill.c | 11 +++++++++++ 2 files changed, 12 insertions(+) diff --git a/include/linux/sched.h b/include/linux/sched.h index 977cb57..58eff50 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -723,6 +723,7 @@ struct task_struct { #endif #ifdef CONFIG_MEMCG unsigned in_user_fault:1; + unsigned memcg_oom_no_eligible_warned:1; #ifdef CONFIG_MEMCG_KMEM unsigned memcg_kmem_skip_account:1; #endif diff --git a/mm/oom_kill.c b/mm/oom_kill.c index f10aa53..ff0fa65 100644 --- a/mm/oom_kill.c +++ b/mm/oom_kill.c @@ -1106,6 +1106,13 @@ bool out_of_memory(struct oom_control *oc) select_bad_process(oc); /* Found nothing?!?! */ if (!oc->chosen) { +#ifdef CONFIG_MEMCG + if (is_memcg_oom(oc)) { + if (current->memcg_oom_no_eligible_warned) + return false; + current->memcg_oom_no_eligible_warned = 1; + } +#endif dump_header(oc, NULL); pr_warn("Out of memory and no killable processes...\n"); /* @@ -1115,6 +1122,10 @@ bool out_of_memory(struct oom_control *oc) */ if (!is_sysrq_oom(oc) && !is_memcg_oom(oc)) panic("System is deadlocked on memory\n"); +#ifdef CONFIG_MEMCG + } else if (is_memcg_oom(oc)) { + current->memcg_oom_no_eligible_warned = 0; +#endif } if (oc->chosen && oc->chosen != (void *)-1UL) oom_kill_process(oc, !is_memcg_oom(oc) ? "Out of memory" : -- 1.8.3.1