linux-kernel - Re: PROBLEM: Kernel 6.17 newly deadlocks futex

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Message-Id: <8c32217d-d4bc-4b82-961a-223813015307@app.fastmail.com>
Date: Mon, 19 Jan 2026 19:24:02 +0100
From: "Florian Albertz" <linux@...m.net>
To: "Sebastian Andrzej Siewior" <bigeasy@...utronix.de>,
 "Thomas Gleixner" <tglx@...utronix.de>
Cc: mingo@...hat.com, linux-kernel@...r.kernel.org,
 "Peter Zijlstra" <peterz@...radead.org>
Subject: Re: PROBLEM: Kernel 6.17 newly deadlocks futex

On Fri, Jan 9, 2026, at 17:56, Sebastian Andrzej Siewior wrote:
> Who is doing this? Some exotic early container runtime?

Personally, I built an abstraction which behaves similarly to how rust does threads, while allowing to configure the namespaces for each of those "threads". Which makes working with namespaces way more ergonomic because changing namespaces is not an all-or-nothing proposition for a binary anymore.

We can run a single function in another network namespace without having to exec an entirely different binary for example. And ideally we can still use in-process synchronization primitives to make this properly useful.

The _PRIVATE flags come into the picture because they are used by rusts standard library and it would be nice if we could use the languages default synchronization primitives. So other code can be mostly oblivious to whether it is used across such a fake-thread boundary or not.

I get that this is probably a pretty weird way to use these APIs, but it IS incredibly useful when having to deal with namespaces a lot. And you guessed correctly, that in my case this happens to be while container tooling.

>> Thanks,
>> 
>>         tglx
>
> Sebastian

Thanks to both of you,
Florian A.