syzbot has bisected this bug to:

commit 46eb14a6e1585d99c1b9f58d0e7389082a5f466b
Author: Pete Zaitcev <zaitcev@redhat.com>
Date:   Mon Jan 8 21:46:41 2018 +0000

     USB: fix usbmon BUG trigger

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=14deb012e00000
start commit:   58c3f14f Merge tag 'riscv-for-linus-4.19-rc2' of git://git..
git tree:       upstream
final crash:    https://syzkaller.appspot.com/x/report.txt?x=16deb012e00000
console output: https://syzkaller.appspot.com/x/log.txt?x=12deb012e00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=531a917630d2a492
dashboard link: https://syzkaller.appspot.com/bug?extid=56f9673bb4cdcbeb0e92
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=13dca13e400000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17cbe492400000

Reported-by: syzbot+56f9673bb4cdcbeb0e92@syzkaller.appspotmail.com
Fixes: 46eb14a6e158 ("USB: fix usbmon BUG trigger")

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