linux-kernel - Re: kernel BUG at kernel/futex.c:679 on v4.13-rc3-ish on arm64

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Date:   Tue, 8 Aug 2017 09:06:48 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Mel Gorman <mgorman@...e.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Davidlohr Bueso <dbueso@...e.de>,
        Thomas Gleixner <tglx@...utronix.de>, Chris Mason <clm@...com>,
        Darren Hart <dvhart@...ux.intel.com>,
        Hugh Dickins <hughd@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Davidlohr Bueso <dave@...olabs.net>
Subject: Re: kernel BUG at kernel/futex.c:679 on v4.13-rc3-ish on arm64

On Tue, Aug 8, 2017 at 8:41 AM, Mark Rutland <mark.rutland@....com> wrote:
>
> With my __BUG_FLAGS() issue corrected, the WARN_ON_ONCE() fires once,
> and everything else seems fine. I'll have a go with additional debug
> enabled just in case.

Ok, great, a - mostly - false alarm.

I do wonder if we should just remove even that WARN_ON_ONCE() - I
think it was added to be careful, and the code seems to do the right
thing.

The second WARN_ON_ONCE() (that is marked as "should be impossible")
we might as well leave around. If that one triggers, it's a lot more
interesting.

Mel? No hurry - the nice thing about WARN_ON_ONCE() is that it's just
a single note so it's neither killing the machine(*) nor causing any
real problems.

                Linus

(*) when it works, but presumably it is now fixed on ARM64, and I
expect I'll see a pull request ;).