linux-kernel - Re: [PATCH] proc, oom: do not report alien mms when setting oom_score

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Date:   Tue, 12 Feb 2019 12:56:35 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        David Rientjes <rientjes@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Yong-Taek Lee <ytk.lee@...sung.com>, <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Michal Hocko <mhocko@...e.com>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Subject: Re: [PATCH] proc, oom: do not report alien mms when setting
 oom_score_adj

On Tue, 12 Feb 2019 11:21:29 +0100 Michal Hocko <mhocko@...nel.org> 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] http://lkml.kernel.org/r/97fce864-6f75-bca5-14bc-12c9f890e740@i-love.sakura.ne.jp
> [2] http://lkml.kernel.org/r/20190117155159.GA4087@dhcp22.suse.cz

I think I'll put a cc:stable on this.  Deleting a might-trigger debug
printk is safe and welcome.