Re: [PATCH] proc, oom: do not report alien mms when setting oom_score_adj

From: Tetsuo Handa
Date: Tue Feb 12 2019 - 16:07:35 EST

On 2019/02/13 5:56, Andrew Morton wrote:
> On Tue, 12 Feb 2019 11:21:29 +0100 Michal Hocko <mhocko@xxxxxxxxxx> wrote:
>> Tetsuo has reported that creating a thousands of processes sharing MM
>> without SIGHAND (aka alien threads) and setting
>> /proc/<pid>/oom_score_adj will swamp the kernel log and takes ages [1]
>> to finish. This is especially worrisome that all that printing is done
>> under RCU lock and this can potentially trigger RCU stall or softlockup
>> detector.
>> The primary reason for the printk was to catch potential users who might
>> depend on the behavior prior to 44a70adec910 ("mm, oom_adj: make sure
>> processes sharing mm have same view of oom_score_adj") but after more
>> than 2 years without a single report I guess it is safe to simply remove
>> the printk altogether.
>> The next step should be moving oom_score_adj over to the mm struct and
>> remove all the tasks crawling as suggested by [2]
>> [1]
>> [2]
> I think I'll put a cc:stable on this. Deleting a might-trigger debug
> printk is safe and welcome.

Putting cc:stable is fine. But I doubt the usefulness of this patch.
If nobody really depends on the behavior prior to 44a70adec910,
we should remove the pointless (otherwise racy) iteration itself.