linux-kernel - Re: [syzbot] [btrfs?] BUG: MAX_LOCKDEP_CHAIN

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Message-ID: <20231023143637.GI26353@suse.cz>
Date:   Mon, 23 Oct 2023 16:36:37 +0200
From:   David Sterba <dsterba@...e.cz>
To:     Aleksandr Nogikh <nogikh@...gle.com>
Cc:     syzbot <syzbot+b2869947e0c9467a41b6@...kaller.appspotmail.com>,
        clm@...com, dsterba@...e.com, josef@...icpanda.com,
        linux-btrfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [syzbot] [btrfs?] BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low! (4)

On Mon, Oct 23, 2023 at 03:30:16PM +0200, Aleksandr Nogikh wrote:
> On Mon, Oct 23, 2023 at 3:15 PM David Sterba <dsterba@...e.cz> wrote:
> >
> > On Sat, Oct 21, 2023 at 07:40:53PM -0700, syzbot wrote:
> > > Hello,
> > >
> > > syzbot found the following issue on:
> > >
> > > HEAD commit:    78124b0c1d10 Merge branch 'for-next/core' into for-kernelci
> > > git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci
> > > console output: https://syzkaller.appspot.com/x/log.txt?x=1557da89680000
> > > kernel config:  https://syzkaller.appspot.com/x/.config?x=f27cd6e68911e026
> > > dashboard link: https://syzkaller.appspot.com/bug?extid=b2869947e0c9467a41b6
> > > compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> > > userspace arch: arm64
> > > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=137ac45d680000
> > > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16e4640b680000
> > >
> > > Downloadable assets:
> > > disk image: https://storage.googleapis.com/syzbot-assets/bd512de820ae/disk-78124b0c.raw.xz
> > > vmlinux: https://storage.googleapis.com/syzbot-assets/a47a437b1d4f/vmlinux-78124b0c.xz
> > > kernel image: https://storage.googleapis.com/syzbot-assets/3ae8b966bcd7/Image-78124b0c.gz.xz
> > > mounted in repro: https://storage.googleapis.com/syzbot-assets/d5d514495f15/mount_0.gz
> > >
> > > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > > Reported-by: syzbot+b2869947e0c9467a41b6@...kaller.appspotmail.com
> > >
> > > BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low!
> >
> > #syz invalid
> >
> > This is a frequent warning, can be worked around by increasing
> > CONFIG_LOCKDEP_CHAINS_BITS in config (18 could be a good value but may
> > still not be enough).
> 
> By invalidating a frequently occurring issue we only cause syzbot to
> report it once again, so it's better to keep the report open until the
> root cause is resolved. There'll likely be a report (5) soon.

The root cause is somewhere in lockdep and not easy to fix so we'll have
to see the duplicate reports or

> We keep CONFIG_LOCKDEP_CHAINS_BITS at 16 for arm64 because (at least
> in 2022) the kernel used not to boot on GCE arm64 VMs with
> CONFIG_LOCKDEP_CHAINS_BITS=18. Maybe it's time to try it once more.

yeah, you can increase the config value.