linux-kernel - Re: [PATCH] mm,page_alloc: PF_WQ_WORKER threads must sleep at should_reclaim

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Message-ID: <20180731111519.GH4557@dhcp22.suse.cz>
Date:   Tue, 31 Jul 2018 13:15:19 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     Tejun Heo <tj@...nel.org>, Roman Gushchin <guro@...com>,
        Johannes Weiner <hannes@...xchg.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        David Rientjes <rientjes@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm,page_alloc: PF_WQ_WORKER threads must sleep at
 should_reclaim_retry().

On Tue 31-07-18 19:47:45, Tetsuo Handa wrote:
> On 2018/07/31 14:09, Michal Hocko wrote:
> > On Tue 31-07-18 06:01:48, Tetsuo Handa wrote:
> >> On 2018/07/31 4:10, Michal Hocko wrote:
> >>> Since should_reclaim_retry() should be a natural reschedule point,
> >>> let's do the short sleep for PF_WQ_WORKER threads unconditionally in
> >>> order to guarantee that other pending work items are started. This will
> >>> workaround this problem and it is less fragile than hunting down when
> >>> the sleep is missed. E.g. we used to have a sleeping point in the oom
> >>> path but this has been removed recently because it caused other issues.
> >>> Having a single sleeping point is more robust.
> >>
> >> linux.git has not removed the sleeping point in the OOM path yet. Since removing the
> >> sleeping point in the OOM path can mitigate CVE-2016-10723, please do so immediately.
> > 
> > is this an {Acked,Reviewed,Tested}-by?
> 
> I'm saying that "we used to have a sleeping point in the oom path but this has been
> removed recently" is not true. You need to send that patch to linux.git first if you
> want to refer that patch in this patch.

That patch is already sitting in mmotm tree and this one will go on top.
I do not really see any reason to rush it to Linus tree. A dubious CVE
doesn't really raise the priority if you ask me.

On the other hand, having a confirmation, either of the above tags would
help to raise the credibility of the change.

> > I will send the patch to Andrew if the patch is ok. 
> 
> Andrew, can we send the "we used to have a sleeping point in the oom path but this has
> been removed recently" patch to linux.git ?

This can really wait for the next merge window IMHO.
-- 
Michal Hocko
SUSE Labs