syzbot has bisected this bug to:

commit 1548bc4e0512700cf757192c106b3a20ab639223
Author: Florian Westphal [off-list ref]
Date:   Fri Jan 4 13:17:02 2019 +0000

     xfrm: policy: delete inexact policies from inexact list on hash rebuild

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1734cba9a00000
start commit:   249155c2 Merge branch 'parisc-5.2-4' of git://git.kernel.o..
git tree:       upstream
final crash:    https://syzkaller.appspot.com/x/report.txt?x=14b4cba9a00000
console output: https://syzkaller.appspot.com/x/log.txt?x=10b4cba9a00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=9a31528e58cc12e2
dashboard link: https://syzkaller.appspot.com/bug?extid=0165480d4ef07360eeda
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=16cf37c3a00000

Reported-by: syzbot+0165480d4ef07360eeda@syzkaller.appspotmail.com
Fixes: 1548bc4e0512 ("xfrm: policy: delete inexact policies from inexact  
list on hash rebuild")

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