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

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Message-ID: <20160531225303.GE26582@redhat.com>
Date:	Wed, 1 Jun 2016 00:53:03 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Michal Hocko <mhocko@...nel.org>
Cc:	linux-mm@...ck.org,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	David Rientjes <rientjes@...gle.com>,
	Vladimir Davydov <vdavydov@...allels.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/6] proc, oom: drop bogus task_lock and mm check

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.

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 ;)

Oleg.