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

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Message-ID: <20240821201338.GA2109582@perftesting>
Date: Wed, 21 Aug 2024 16:13:38 -0400
From: Josef Bacik <josef@...icpanda.com>
To: syzbot <syzbot+dfb6eff2a68b42d557d3@...kaller.appspotmail.com>
Cc: clm@...com, dsterba@...e.com, linux-btrfs@...r.kernel.org,
	linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [btrfs?] BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low! (6)

On Wed, Aug 21, 2024 at 12:45:25PM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    5c43d43bad35 Merge branches 'for-next/acpi', 'for-next/mis..
> 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=13471a05980000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=c91f83ae59feaa1f
> dashboard link: https://syzkaller.appspot.com/bug?extid=dfb6eff2a68b42d557d3
> 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=10efded5980000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=12e94093980000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/cc2dd4be620e/disk-5c43d43b.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/81d40d99ddbf/vmlinux-5c43d43b.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/bc6aed0f2bc5/Image-5c43d43b.gz.xz
> mounted in repro: https://storage.googleapis.com/syzbot-assets/d55321fffedc/mount_0.gz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+dfb6eff2a68b42d557d3@...kaller.appspotmail.com
> 
> BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low!

Can we disable syzbot issues for this specific error?  Btrfs uses lockdep
annotations for our tree locks, so we _easily_ cross this threshold on the
default configuration.  Our CI config requires the following settings to get
lockdep to work longer than two or three tests

CONFIG_LOCKDEP_BITS=20
CONFIG_LOCKDEP_CHAINS_BITS=20
CONFIG_LOCKDEP_STACK_TRACE_BITS=19
CONFIG_LOCKDEP_STACK_TRACE_HASH_BITS=14
CONFIG_LOCKDEP_CIRCULAR_QUEUE_BITS=12

but there's no way to require that in our config (nor do I think we should
really be able to tbqh).  It makes more sense for syzbot to just ignore this
particular error as it's not actually a bug.  Thanks,

Josef