syzbot has bisected this bug to:

commit f4b3526d83c40dd8bf5948b9d7a1b2c340f0dcc8
Author: David Howells [off-list ref]
Date:   Thu Nov 2 15:27:48 2017 +0000

    afs: Connect up the CB.ProbeUuid

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1627a721e00000
start commit:   d96d875e Merge tag 'fixes_for_v5.5-rc8' of git://git.kerne..
git tree:       upstream
final crash:    https://syzkaller.appspot.com/x/report.txt?x=1527a721e00000
console output: https://syzkaller.appspot.com/x/log.txt?x=1127a721e00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=83c00afca9cf5153
dashboard link: https://syzkaller.appspot.com/bug?extid=b904ba7c947a37b4b291
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12c96185e00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=14f859c9e00000

Reported-by: syzbot+b904ba7c947a37b4b291@syzkaller.appspotmail.com
Fixes: f4b3526d83c4 ("afs: Connect up the CB.ProbeUuid")

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