linux-kernel - Re: [PATCH 1/6] proc, oom: drop bogus task

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Message-Id: <201606011941.DJJ09369.FSFtQVMLFOJOOH@I-love.SAKURA.ne.jp>
Date:	Wed, 1 Jun 2016 19:41:09 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	mhocko@...nel.org, oleg@...hat.com
Cc:	linux-mm@...ck.org, rientjes@...gle.com, vdavydov@...allels.com,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/6] proc, oom: drop bogus task_lock and mm check

Michal Hocko wrote:
> On Wed 01-06-16 00:53:03, Oleg Nesterov wrote:
> > On 05/31, Michal Hocko wrote:
> > >
> > > Oleg has pointed out that can simplify both oom_adj_write and
> > > oom_score_adj_write even further and drop the sighand lock. The only
> > > purpose of the lock was to protect p->signal from going away but this
> > > will not happen since ea6d290ca34c ("signals: make task_struct->signal
> > > immutable/refcountable").
> > 
> > Sorry for confusion, I meant oom_adj_read() and oom_score_adj_read().
> > 
> > As for oom_adj_write/oom_score_adj_write we can remove it too, but then
> > we need to ensure (say, using cmpxchg) that unpriviliged user can not
> > not decrease signal->oom_score_adj_min if its oom_score_adj_write()
> > races with someone else (say, admin) which tries to increase the same
> > oom_score_adj_min.
> 
> I am introducing oom_adj_mutex in a later patch so I will move it here.

Can't we reuse oom_lock like

	if (mutex_lock_killable(&oom_lock))
		return -EINTR;

? I think that updating oom_score_adj unlikely races with OOM killer
invocation, and updating oom_score_adj should be a killable operation.

> 
> > If you think this is not a problem - I am fine with this change. But
> > please also update oom_adj_read/oom_score_adj_read ;)
> 
> will do. It stayed in the blind spot... Thanks for pointing that out
> 
> Thanks!
> -- 
> Michal Hocko
> SUSE Labs
>