From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f71.google.com (mail-ed1-f71.google.com [209.85.208.71]) by kanga.kvack.org (Postfix) with ESMTP id 192736B0007 for ; Mon, 25 Jun 2018 09:07:59 -0400 (EDT) Received: by mail-ed1-f71.google.com with SMTP id i19-v6so2313643eds.20 for ; Mon, 25 Jun 2018 06:07:59 -0700 (PDT) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id i5-v6si6297378edg.99.2018.06.25.06.07.57 for (version=TLS1 cipher=AES128-SHA bits=128/128); Mon, 25 Jun 2018 06:07:57 -0700 (PDT) Date: Mon, 25 Jun 2018 15:07:56 +0200 From: Michal Hocko Subject: Re: [PATCH] mm,oom: Bring OOM notifier callbacks to outside of OOM killer. Message-ID: <20180625130756.GK28965@dhcp22.suse.cz> References: <1529493638-6389-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp> <20180620115531.GL13685@dhcp22.suse.cz> <3d27f26e-68ba-d3c0-9518-cebeb2689aec@sony.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <3d27f26e-68ba-d3c0-9518-cebeb2689aec@sony.com> Sender: owner-linux-mm@kvack.org List-ID: To: peter enderborg Cc: Tetsuo Handa , linux-mm@kvack.org, rientjes@google.com, akpm@linux-foundation.org, linux-kernel@vger.kernel.org On Mon 25-06-18 15:03:40, peter enderborg wrote: > On 06/20/2018 01:55 PM, Michal Hocko wrote: > > 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. > > It is a mutex you are supposed to be able to sleep. It's even exported. What do you mean? oom_lock is certainly not exported for general use. It is not local to oom_killer.c just because it is needed in other _mm_ code. > >> 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? > > > @Hocko Do you remember the lowmemorykiller from android? Some things > might not be the right thing for shrinkers. Just that lmk did it wrong doesn't mean others have to follow. -- Michal Hocko SUSE Labs