syzbot has bisected this bug to:

commit e3933f26b657c341055443103bad331f4537b113
Author: Rex Zhu [off-list ref]
Date:   Tue Jan 16 10:35:15 2018 +0000

     drm/amd/pp: Add edit/commit/show OD clock/voltage support in sysfs

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?xb5a799e00000
start commit:   c6017471 Merge tag 'xfs-5.5-fixes-2' of git://git.kernel.o..
git tree:       upstream
final crash:    https://syzkaller.appspot.com/x/report.txt?xb5a799e00000
console output: https://syzkaller.appspot.com/x/log.txt?xb5a799e00000
kernel config:  https://syzkaller.appspot.com/x/.config?x6119e2e3675a73
dashboard link: https://syzkaller.appspot.com/bug?extidÑ30c4a0890561cfac5b
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x9b1925e00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?xb9623ee00000

Reported-by: syzbot+d130c4a0890561cfac5b@syzkaller.appspotmail.com
Fixes: e3933f26b657 ("drm/amd/pp: Add edit/commit/show OD clock/voltage  
support in sysfs")

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