syzbot has bisected this issue to:

commit 741ec653ab58f5f263f2b6df38157997661c7a50
Author: Qu Wenruo [off-list ref]
Date:   Mon Sep 27 07:22:01 2021 +0000

    btrfs: subpage: make end_compressed_bio_writeback() compatible

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=103f2ae5b00000
start commit:   cd8c917a56f2 Makefile: Do not quote value for CONFIG_CC_IM..
git tree:       upstream
final oops:     https://syzkaller.appspot.com/x/report.txt?x=123f2ae5b00000
console output: https://syzkaller.appspot.com/x/log.txt?x=143f2ae5b00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=5247c9e141823545
dashboard link: https://syzkaller.appspot.com/bug?extid=21e6887c0be14181206d
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1218dce1b00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16f91d89b00000

Reported-by: syzbot+21e6887c0be14181206d@syzkaller.appspotmail.com
Fixes: 741ec653ab58 ("btrfs: subpage: make end_compressed_bio_writeback() compatible")

For information about bisection process see: https://goo.gl/tpsmEJ#bisection