[syzbot] kernel BUG in vmf_insert_pfn_prot

[syzbot]

syzbot has bisected this issue to:

commit 8b93d1d7dbd578fd296e70008b29c0f62d09d7cb
Author: Daniel Vetter <daniel.vetter at ffwll.ch>
Date:   Thu Aug 12 13:14:10 2021 +0000

    drm/shmem-helper: Switch to vmf_insert_pfn

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1277054f300000
start commit:   9004fd387338 Add linux-next specific files for 20210917
git tree:       linux-next
final oops:     https://syzkaller.appspot.com/x/report.txt?x=1177054f300000
console output: https://syzkaller.appspot.com/x/log.txt?x=1677054f300000
kernel config:  https://syzkaller.appspot.com/x/.config?x=45d5ac72f31f29f3
dashboard link: https://syzkaller.appspot.com/bug?extid=2d4f8693f438d2bd4bdb
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=13ad5527300000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13beef77300000

Reported-by: syzbot+2d4f8693f438d2bd4bdb at syzkaller.appspotmail.com
Fixes: 8b93d1d7dbd5 ("drm/shmem-helper: Switch to vmf_insert_pfn")

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