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From:   Mikael Pettersson <mikpelinux@gmail.com>
Date:   Mon, 9 Aug 2021 15:31:33 +0200
Message-ID: <CAM43=SO03vCzo4LiwSFJyNbWdVXu_wu1gdm5wzi2ArsWShCqqA@mail.gmail.com>
Subject: Re: [BISECTED][REGRESSION] 5.10.56 longterm kernel breakage on m68k/aranym
To:     Finn Thain <fthain@linux-m68k.org>
Cc:     Linux Kernel list <linux-kernel@vger.kernel.org>,
        linux-m68k@lists.linux-m68k.org, stable@vger.kernel.org,
        Peter Xu <peterx@redhat.com>
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On Mon, Aug 9, 2021 at 3:59 AM Finn Thain <fthain@linux-m68k.org> wrote:
>
> On Sun, 8 Aug 2021, Mikael Pettersson wrote:
>
> > On Sun, Aug 8, 2021 at 1:20 AM Finn Thain <fthain@linux-m68k.org> wrote:
> > >
> > > On Sat, 7 Aug 2021, Mikael Pettersson wrote:
> > >
> > > > I updated the 5.10 longterm kernel on one of my m68k/aranym VMs from
> > > > 5.10.47 to 5.10.56, and the new kernel failed to boot:
> > > >
> > > > ARAnyM 1.1.0
> > > > Using config file: 'aranym1.headless.config'
> > > > Could not open joystick 0
> > > > ARAnyM RTC Timer: /dev/rtc: Permission denied
> > > > ARAnyM LILO: Error loading ramdisk 'root.bin'
> > > > Blitter tried to read byte from register ff8a00 at 0077ee
> > > >
> > > > At this point it kept running, but produced no output to the console,
> > > > and would never get to the point of starting user-space. Attaching gdb
> > > > to aranym showed nothing interesting, i.e. it seemed to be executing
> > > > normally.
> > > >
> > > > A git bisect identified the following commit between 5.10.52 and
> > > > 5.10.53 as the culprit:
> > > > # first bad commit: [9e1cf2d1ed37c934c9935f2c0b2f8b15d9355654]
> > > > mm/userfaultfd: fix uffd-wp special cases for fork()
> > > >
> > >
> > > That commit appeared in mainline between v5.13 and v5.14-rc1. Is mainline
> > > also affected? e.g. v5.14-rc4.
> >
> > 5.14-rc4 boots fine. I suspect the commit has some dependency that
> > hasn't been backported to 5.10 stable.
> >
>
> On mainline, 9e1cf2d1ed3 is known as commit 8f34f1eac382 ("mm/userfaultfd:
> fix uffd-wp special cases for fork()").
>
> There are differences between the two commits that may be relevant. I
> don't know.
>
> If you checkout 8f34f1eac382 and if that works, it would indicate either
> missing dependencies in -stable, or those differences are important.
>
> OTOH, if 8f34f1eac382 fails in the same way as linux-5.10.y, it would
> indicate that -stable is missing a fix that's present in v5.14-rc4.

My initial bisect was wrong. I tried reverting 8f34f1eac382 from
5.10.57 but that made no difference, so I re-ran the git bisect with
all known good points pre-marked. This landed on:
# first bad commit: [ce6ee46e0f39ed97e23ebf7b5a565e0266a8a1a3]
mm/page_alloc: fix memory map initialization for descending nodes

Reverting _that_ from 5.10.57 does unbreak that kernel.

Sorry about the confusion.