linux-kernel - Re: [syzbot] [bcachefs?] general protection fault in proc_sys

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Message-ID: <ph6whomevsnlsndjuewjxaxi6ngezbnlmv2hmutlygrdu37k3w@k57yfx76ptih>
Date: Fri, 7 Mar 2025 06:51:23 -0500
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: Hector Martin <marcan@...can.st>
Cc: syzbot <syzbot+4364ec1693041cad20de@...kaller.appspotmail.com>, 
	broonie@...nel.org, joel.granados@...nel.org, kees@...nel.org, 
	linux-bcachefs@...r.kernel.org, linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, 
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [bcachefs?] general protection fault in proc_sys_compare

On Fri, Mar 07, 2025 at 08:20:37PM +0900, Hector Martin wrote:
> On 2025/03/07 11:45, syzbot wrote:
> > Hello,
> > 
> > syzbot found the following issue on:
> > 
> > HEAD commit:    b91872c56940 Merge tag 'dmaengine-fix-6.14' of git://git.k..
> > git tree:       upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=1485e8b7980000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=8de9cc84d5960254
> > dashboard link: https://syzkaller.appspot.com/bug?extid=4364ec1693041cad20de
> > compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=149d55a8580000
> > 
> > Downloadable assets:
> > disk image: https://storage.googleapis.com/syzbot-assets/4b855669df70/disk-b91872c5.raw.xz
> > vmlinux: https://storage.googleapis.com/syzbot-assets/e44f3c546271/vmlinux-b91872c5.xz
> > kernel image: https://storage.googleapis.com/syzbot-assets/b106e670346a/bzImage-b91872c5.xz
> > mounted in repro: https://storage.googleapis.com/syzbot-assets/68b26fa478ee/mount_0.gz
> > 
> > The issue was bisected to:
> > 
> > commit 579cd64b9df8a60284ec3422be919c362de40e41
> > Author: Hector Martin <marcan@...can.st>
> > Date:   Sat Feb 8 00:54:35 2025 +0000
> > 
> >     ASoC: tas2770: Fix volume scale
> > 
> > bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=14aa03a8580000
> > final oops:     https://syzkaller.appspot.com/x/report.txt?x=16aa03a8580000
> > console output: https://syzkaller.appspot.com/x/log.txt?x=12aa03a8580000
> [...]
> 
> This is a bad bisect. Not sure what the appropriate syzbot action is in
> this case.

Better bisection algorithm? Standand bisect does really badly when fed
noisy data, but it wouldn't be hard to fix that: after N successive
passes or fails, which is unlikely because bisect tests are coinflips,
backtrack and gather more data in the part of the commit history where
you don't have much.