From: Nico Pache <npache@redhat.com>
To: Thomas Gleixner <tglx@linutronix.de>,
Peter Zijlstra <peterz@infradead.org>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Rafael Aquini <aquini@redhat.com>,
Waiman Long <longman@redhat.com>, Baoquan He <bhe@redhat.com>,
Christoph von Recklinghausen <crecklin@redhat.com>,
Don Dutile <ddutile@redhat.com>,
"Herton R . Krzesinski" <herton@redhat.com>,
David Rientjes <rientjes@google.com>,
Michal Hocko <mhocko@suse.com>,
Andrea Arcangeli <aarcange@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>,
Davidlohr Bueso <dave@stgolabs.net>,
Ingo Molnar <mingo@redhat.com>, Joel Savitz <jsavitz@redhat.com>,
Darren Hart <dvhart@infradead.org>,
stable@kernel.org
Subject: Re: [PATCH v8] oom_kill.c: futex: Don't OOM reap the VMA containing the robust_list_head
Date: Fri, 8 Apr 2022 04:52:33 -0400 [thread overview]
Message-ID: <ddf1755e-fe69-b60e-ee07-e78d663b11b2@redhat.com> (raw)
In-Reply-To: <87tub4j7hg.ffs@tglx>
On 4/8/22 04:37, Thomas Gleixner wrote:
> 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?
We've tried multiple approaches to reproduce the case you are talking about with
no success...
Why make a change for something that we cant reproduce when we are sure this
works for all the cases we've attempted.
I also dont see how this a broken heuristic... If anything adding a delay is
broken. How do we assure the delay is long enough for the exit to clean up the
futexes? In a heavily contended CPU with high memory pressure the delay may also
lead to other processes unnecessarily OOMing.
Cheers,
-- Nico
>
> Thanks,
>
> tglx
>
>
next prev parent reply other threads:[~2022-04-08 8:52 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-08 3:28 [PATCH v8] oom_kill.c: futex: Don't OOM reap the VMA containing the robust_list_head Nico Pache
2022-04-08 8:15 ` Peter Zijlstra
2022-04-08 8:37 ` Thomas Gleixner
2022-04-08 8:52 ` Nico Pache [this message]
2022-04-08 9:36 ` Michal Hocko
2022-04-08 9:40 ` Nico Pache
2022-04-08 9:59 ` Michal Hocko
2022-04-08 10:36 ` Nico Pache
2022-04-08 10:51 ` Michal Hocko
2022-04-08 11:26 ` Nico Pache
2022-04-08 11:48 ` Michal Hocko
2022-04-08 8:41 ` Nico Pache
2022-04-08 13:54 ` Thomas Gleixner
2022-04-08 16:13 ` Joel Savitz
2022-04-08 21:41 ` Thomas Gleixner
2022-04-11 6:48 ` Michal Hocko
2022-04-11 7:47 ` Thomas Gleixner
2022-04-11 9:08 ` Michal Hocko
2022-04-12 0:02 ` Nico Pache
2022-04-13 16:00 ` Nico Pache
2022-04-11 23:51 ` Nico Pache
2022-04-12 16:20 ` Thomas Gleixner
2022-04-12 17:03 ` Nico Pache
2022-04-08 14:41 ` kernel test robot
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