linux-kernel - Re: [PATCH v4 2/3] mm/oom_kill: Only delay OOM reaper for processes using robust futexes

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <20250820025308.rkqlvauh4dz42oic@offworld>
Date: Tue, 19 Aug 2025 19:53:08 -0700
From: Davidlohr Bueso <dave@...olabs.net>
To: Michal Hocko <mhocko@...e.com>
Cc: zhongjinji <zhongjinji@...or.com>, akpm@...ux-foundation.org,
	andrealmeid@...lia.com, dvhart@...radead.org, feng.han@...or.com,
	liam.howlett@...cle.com, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, liulu.liu@...or.com, mingo@...hat.com,
	npache@...hat.com, peterz@...radead.org, rientjes@...gle.com,
	shakeel.butt@...ux.dev, tglx@...utronix.de
Subject: Re: [PATCH v4 2/3] mm/oom_kill: Only delay OOM reaper for processes
 using robust futexes

On Tue, 19 Aug 2025, Michal Hocko wrote:

>On Mon 18-08-25 20:08:19, zhongjinji wrote:
>> If a process holding robust futexes gets frozen, robust futexes might be reaped before
>> futex_cleanup() runs when an OOM occurs. I am not sure if this will actually happen.
>
>Yes, and 2s delay will never rule that out. Especially for frozen tasks
>which could be frozen undefinitely. That is not the point I have tried
>to make. I was suggesting not treating futex specially because no matter
>what we do this will always be racy and a hack to reduce the risk. We
>simply cannot deal with that case more gracefully without a major
>surgery to the futex implementation which is not desirable for this
>specific reason.

Yeah, relying on time as a fix is never a good idea. I was going to suggest
skipping the reaping for tasks with a robust list, but that still requires
the racy check, and your suggested workaround seems more practical.

Thanks,
Davidlohr