syzbot suspects this issue was fixed by commit:

commit 282ab3ff16120ec670fe3330e85f8ebf13092f21
Author: David Sterba [off-list ref]
Date:   Mon Oct 14 12:38:33 2019 +0000

    btrfs: reduce compressed_bio members' types

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=12d5f6f2300000
start commit:   7f75285ca572 Merge tag 'for-5.12/dm-fixes-3' of git://git...
git tree:       upstream
kernel config:  https://syzkaller.appspot.com/x/.config?x=b5591c832f889fd9
dashboard link: https://syzkaller.appspot.com/bug?extid=45d7c243c006f39dc55a
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=164f385ad00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1427af9ad00000

If the result looks correct, please mark the issue as fixed by replying with:

#syz fix: btrfs: reduce compressed_bio members' types

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