syzbot has bisected this bug to:

commit 0a957467c5fd46142bc9c52758ffc552d4c5e2f7
Author: Guenter Roeck [off-list ref]
Date:   Wed Aug 15 20:22:27 2018 +0000

     x86: i8259: Add missing include file

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1579e751e00000
start commit:   46cf053e Linux 5.5-rc3
git tree:       upstream
final crash:    https://syzkaller.appspot.com/x/report.txt?x=1779e751e00000
console output: https://syzkaller.appspot.com/x/log.txt?x=1379e751e00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=ed9d672709340e35
dashboard link: https://syzkaller.appspot.com/bug?extid=19616eedf6fd8e241e50
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14a47ab9e00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=170f2485e00000

Reported-by: syzbot+19616eedf6fd8e241e50@syzkaller.appspotmail.com
Fixes: 0a957467c5fd ("x86: i8259: Add missing include file")

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