linux-kernel - Re: [syzbot] [mm?] WARNING in vma_merge_existing

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Message-ID: <CACT4Y+aVqKnbp0HbyaboeEUxM1baXkX=6Q2UcMHN+fSzFQDUGQ@mail.gmail.com>
Date: Tue, 7 Jan 2025 09:14:54 +0100
From: Dmitry Vyukov <dvyukov@...gle.com>
To: Aleksandr Nogikh <nogikh@...gle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, 
	syzbot <syzbot+46423ed8fa1f1148c6e4@...kaller.appspotmail.com>, 
	Liam.Howlett@...cle.com, akpm@...ux-foundation.org, jannh@...gle.com, 
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, 
	syzkaller-bugs@...glegroups.com, vbabka@...e.cz
Subject: Re: [syzbot] [mm?] WARNING in vma_merge_existing_range

On Thu, 2 Jan 2025 at 18:19, 'Aleksandr Nogikh' via syzkaller-bugs
<syzkaller-bugs@...glegroups.com> wrote:
>
> On Thu, Jan 2, 2025 at 11:26 AM 'Lorenzo Stoakes' via syzkaller-bugs
> <syzkaller-bugs@...glegroups.com> wrote:
> >
> > Happy new year!
>
> Happy New Year! :)
>
> >
> > On Tue, Dec 31, 2024 at 08:50:23PM -0800, syzbot wrote:
> > > Hello,
> > >
> > > syzbot found the following issue on:
> > >
> > > HEAD commit:    8379578b11d5 Merge tag 'for-v6.13-rc' of git://git.kernel...
> > > git tree:       upstream
> > > console output: https://syzkaller.appspot.com/x/log.txt?x=16113018580000
> > > kernel config:  https://syzkaller.appspot.com/x/.config?x=d269ef41b9262400
> > > dashboard link: https://syzkaller.appspot.com/bug?extid=46423ed8fa1f1148c6e4
> > > compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> > > userspace arch: i386
> >
> > Hmmmm 32-bit? But kernel reports give 64-bit registers? So I guess 32-bit
> > userland, 64-bit kernel?
>
> Yes, that's a 32-bit userspace binary running on a 64-bit kernel.
>
> >
> > >
> > > Unfortunately, I don't have any reproducer for this issue yet.
> >
> > Hmm. Racey thing?
> >
> > >
> > > Downloadable assets:
> > > disk image: https://storage.googleapis.com/syzbot-assets/86d2e3352aff/disk-8379578b.raw.xz
> > > vmlinux: https://storage.googleapis.com/syzbot-assets/345570cd3573/vmlinux-8379578b.xz
> > > kernel image: https://storage.googleapis.com/syzbot-assets/01da37a51505/bzImage-8379578b.xz
> > >
> > > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > > Reported-by: syzbot+46423ed8fa1f1148c6e4@...kaller.appspotmail.com
> > >
> > > RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
> > > R10: 0000000000000000 R11: 0000000000000206 R12: 0000000000000000
> > > R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
> > >  </TASK>
> > > ------------[ cut here ]------------
> > > WARNING: CPU: 1 PID: 20504 at mm/vma.c:734 vma_merge_existing_range+0x1145/0x16f0 mm/vma.c:734
> >
> > It'd be nice if syzbot could actually print the code that generates the
> > warning :) a nice-to-have perhaps.
>
> Thanks for the suggestion!
> I've filed https://github.com/google/syzkaller/issues/5654

It may be better for the kernel to do it. Then it would benefit all
testing systems, and most manual testing/reports as well.
Since WARN_ON is a macro, it should be trivial to capture the
condition string. I guess some embed kernels will want to turn it off,
so probably should be configurable.