linux-kernel - Re: [PATCH] mm,oom: Bring OOM notifier callbacks to outside of OOM killer.

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Message-ID: <20180620115531.GL13685@dhcp22.suse.cz>
Date:   Wed, 20 Jun 2018 13:55:31 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:     linux-mm@...ck.org, rientjes@...gle.com, akpm@...ux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm,oom: Bring OOM notifier callbacks to outside of OOM
 killer.

On Wed 20-06-18 20:20:38, Tetsuo Handa wrote:
> Sleeping with oom_lock held can cause AB-BA lockup bug because
> __alloc_pages_may_oom() does not wait for oom_lock. Since
> blocking_notifier_call_chain() in out_of_memory() might sleep, sleeping
> with oom_lock held is currently an unavoidable problem.

Could you be more specific about the potential deadlock? Sleeping while
holding oom lock is certainly not nice but I do not see how that would
result in a deadlock assuming that the sleeping context doesn't sleep on
the memory allocation obviously.

> As a preparation for not to sleep with oom_lock held, this patch brings
> OOM notifier callbacks to outside of OOM killer, with two small behavior
> changes explained below.

Can we just eliminate this ugliness and remove it altogether? We do not
have that many notifiers. Is there anything fundamental that would
prevent us from moving them to shrinkers instead?
-- 
Michal Hocko
SUSE Labs