Re: [PATCH] mm, oom_adj: avoid meaningless loop to find processes sharing mm

[Tetsuo Handa]

On 2018/10/09 20:10, Michal Hocko wrote:
> On Tue 09-10-18 19:00:44, Tetsuo Handa wrote:
>>> 2) add OOM_SCORE_ADJ_MIN and do not kill tasks sharing mm and do not
>>> reap the mm in the rare case of the race.
>>
>> That is no problem. The mistake we made in 4.6 was that we updated oom_score_adj
>> to -1000 (and allowed unprivileged users to OOM-lockup the system).
> 
> I do not follow.
> 

http://tomoyo.osdn.jp/cgi-bin/lxr/source/mm/oom_kill.c?v=linux-4.6.7#L493

[  177.722853] a.out invoked oom-killer: gfp_mask=0x24280ca(GFP_HIGHUSER_MOVABLE|__GFP_ZERO), order=0, oom_score_adj=0
[  177.724956] a.out cpuset=/ mems_allowed=0
[  177.725735] CPU: 3 PID: 3962 Comm: a.out Not tainted 4.5.0-rc2-next-20160204 #291
(...snipped...)
[  177.802889] [ pid ]   uid  tgid total_vm      rss nr_ptes nr_pmds swapents oom_score_adj name
(...snipped...)
[  177.872248] [ 3941]  1000  3941    28880      124      14       3        0             0 bash
[  177.874279] [ 3962]  1000  3962   541717   395780     784       6        0             0 a.out
[  177.876274] [ 3963]  1000  3963     1078       21       7       3        0          1000 a.out
[  177.878261] [ 3964]  1000  3964     1078       21       7       3        0          1000 a.out
[  177.880194] [ 3965]  1000  3965     1078       21       7       3        0          1000 a.out
[  177.882262] Out of memory: Kill process 3963 (a.out) score 998 or sacrifice child
[  177.884129] Killed process 3963 (a.out) total-vm:4312kB, anon-rss:84kB, file-rss:0kB, shmem-rss:0kB
[  177.887100] oom_reaper: reaped process :3963 (a.out) anon-rss:0kB, file-rss:0kB, shmem-rss:0lB
[  179.638399] crond invoked oom-killer: gfp_mask=0x24201ca(GFP_HIGHUSER_MOVABLE|__GFP_COLD), order=0, oom_score_adj=0
[  179.647708] crond cpuset=/ mems_allowed=0
[  179.652996] CPU: 3 PID: 742 Comm: crond Not tainted 4.5.0-rc2-next-20160204 #291
(...snipped...)
[  179.771311] [ pid ]   uid  tgid total_vm      rss nr_ptes nr_pmds swapents oom_score_adj name
(...snipped...)
[  179.836221] [ 3941]  1000  3941    28880      124      14       3        0             0 bash
[  179.838278] [ 3962]  1000  3962   541717   396308     785       6        0             0 a.out
[  179.840328] [ 3963]  1000  3963     1078        0       7       3        0         -1000 a.out
[  179.842443] [ 3965]  1000  3965     1078        0       7       3        0          1000 a.out
[  179.844557] Out of memory: Kill process 3965 (a.out) score 998 or sacrifice child
[  179.846404] Killed process 3965 (a.out) total-vm:4312kB, anon-rss:0kB, file-rss:0kB, shmem-rss:0kB