syzbot has bisected this bug to:

commit da2648390ce3d409218b6bbbf2386d8ddeec2265
Author: Lubomir Rintel [off-list ref]
Date:   Thu Dec 20 18:13:09 2018 +0000

    pxa168fb: trivial typo fix

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x61e139e00000
start commit:   5076190d mm: slub: be more careful about the double cmpxch..
git tree:       upstream
final crash:    https://syzkaller.appspot.com/x/report.txt?xe1e139e00000
console output: https://syzkaller.appspot.com/x/log.txt?x61e139e00000
kernel config:  https://syzkaller.appspot.com/x/.config?xŸ894bd92023de02
dashboard link: https://syzkaller.appspot.com/bug?extid950016bd95c2ca0377b
userspace arch: i386
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x62bbe3e00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?xc93b45e00000

Reported-by: syzbot+3950016bd95c2ca0377b@syzkaller.appspotmail.com
Fixes: da2648390ce3 ("pxa168fb: trivial typo fix")

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