linux-kernel - Re: WARN_ON_ONCE(!new_owner) within wake_futex

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Date:   Wed, 28 Nov 2018 15:32:45 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Heiko Carstens <heiko.carstens@...ibm.com>
cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org
Subject: Re: WARN_ON_ONCE(!new_owner) within wake_futex_pi() triggered

Heiko,

On Tue, 27 Nov 2018, Heiko Carstens wrote:

> with the glibc self-tests I was able to trigger the "this should not
> happen" warning ;) below on s390 (with panic_on_warn=1 set). It looks
> like it is hardly reproducible.

Any idea which self-test triggered that?

> This one happened with commit d146194f31c9 for compiling the kernel.
> Config can be re-created with "make ARCH=s390 performance_defconfig".

Which is not really helpful for people who do not own a s390. And no, I
don't want one unless IBM pays the power bill as well :)

> [  649.596938] WARNING: CPU: 0 PID: 58886 at kernel/futex.c:1418 do_futex+0xa9a/0xc50
> [  649.596946] Kernel panic - not syncing: panic_on_warn set ...
> [  649.596951] CPU: 0 PID: 58886 Comm: ld64.so.1 Not tainted 4.20.0-20181125.rc3.git0.d146194f31c9.300.fc29.s390x+git #1

That's ld64.so.1. Weird, but what do I know about glibc self tests.

I still fail to see how that can happen, but I usually page out the futex
horrors immediately. I'll keep staring at the code...

Thanks,

	tglx