linux-kernel - Re: [PATCH v3] mm: memcontrol: Don't flood OOM messages with no eligible task.

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Date:   Tue, 23 Oct 2018 09:47:26 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Michal Hocko <mhocko@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>, linux-mm@...ck.org,
        syzkaller-bugs@...glegroups.com, guro@...com,
        kirill.shutemov@...ux.intel.com, linux-kernel@...r.kernel.org,
        rientjes@...gle.com, yang.s@...baba-inc.com,
        Andrew Morton <akpm@...ux-foundation.org>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        syzbot <syzbot+77e6b28a7a7106ad0def@...kaller.appspotmail.com>,
        Calvin Owens <calvinowens@...com>
Subject: Re: [PATCH v3] mm: memcontrol: Don't flood OOM messages with no
 eligible task.

On (10/19/18 19:35), Tetsuo Handa wrote:
> > 
> > OK, that's a fair point. There was a patch from FB, which would allow us
> > to set a log_level on per-console basis. So the noise goes to heav^W net
> > console; only critical stuff goes to the serial console (if I recall it
> > correctly). I'm not sure what happened to that patch, it was a while ago.
> > I'll try to find that out.
> 
> Per a console loglevel setting would help for several environments.
> But syzbot environment cannot count on netconsole. We can't expect that
> unlimited printk() will become safe.

This target is moving too fast :) RCU stall -> user interaction -> syzbot

I talked to Calvin Owens (who's working on the per-console loglevel
patch set; CC-ed) and Calvin said that "It's in-progress". So we probably
will have this functionality one day. That's all we can do from printk
side wrt user-interaction problem.

> > The problem you are talking about is not MM specific. You can have a
> > faulty SCSI device, corrupted FS, and so and on.
> 
> "a faulty SCSI device, corrupted FS, and so and on" are reporting problems
> which will complete a request. They can use (and are using) ratelimit,
> aren't they?

Looking at scsi_request_fn(), the answer is probably "sure they can;
but no, they aren't". In majority of cases the reason we replace printk
with printk_ratelimit is because someone reports a stall or a lockup.
Otherwise, people use printk(), which is absolutely fine.

	-ss