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

[Andrew Morton]

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] http://lkml.kernel.org/r/97fce864-6f75-bca5-14bc-12c9f890e740@xxxxxxxxxxxxxxxxxxx
> [2] http://lkml.kernel.org/r/20190117155159.GA4087@xxxxxxxxxxxxxx

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