linux-kernel - Re: [PATCH v8] oom_kill.c: futex: Don't OOM reap the VMA containing the robust_list

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Date:   Fri, 08 Apr 2022 10:37:47 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>,
        Nico Pache <npache@...hat.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Rafael Aquini <aquini@...hat.com>,
        Waiman Long <longman@...hat.com>, Baoquan He <bhe@...hat.com>,
        Christoph von Recklinghausen <crecklin@...hat.com>,
        Don Dutile <ddutile@...hat.com>,
        "Herton R . Krzesinski" <herton@...hat.com>,
        David Rientjes <rientjes@...gle.com>,
        Michal Hocko <mhocko@...e.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Davidlohr Bueso <dave@...olabs.net>,
        Ingo Molnar <mingo@...hat.com>,
        Joel Savitz <jsavitz@...hat.com>,
        Darren Hart <dvhart@...radead.org>, stable@...nel.org
Subject: Re: [PATCH v8] oom_kill.c: futex: Don't OOM reap the VMA containing
 the robust_list_head

On Fri, Apr 08 2022 at 10:15, Peter Zijlstra wrote:
> On Thu, Apr 07, 2022 at 11:28:09PM -0400, Nico Pache wrote:
>> Theoretically a failure can still occur if there are locks mapped as
>> PRIVATE|ANON; however, the robust futexes are a best-effort approach.
>> This patch only strengthens that best-effort.
>> 
>> The following case can still fail:
>> robust head (skipped) -> private lock (reaped) -> shared lock
>> (skipped)
>
> This is still all sorts of confused.. it's a list head, the entries can
> be in any random other VMA. You must not remove *any* user memory before
> doing the robust thing. Not removing the VMA that contains the head is
> pointless in the extreme.
>
> Did you not read the previous discussion?

Aside of that we all agreed that giving a oom-killed task time to
cleanup itself instead of brute force cleaning it up immediately, which
is the real problem here. Can we fix that first before adding broken
heuristics?

Thanks,

        tglx