WARNING in vkms_vblank_simulate

[syzbot]

syzbot has bisected this bug to:

commit 09ef09b4ab95dc405ad4171ec2cd8a4ff5227108
Author: Shayenne Moura <shayenneluzmoura@xxxxxxxxx>
Date:   Wed Feb 6 20:08:13 2019 +0000

    drm/vkms: WARN when hrtimer_forward_now fails

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=128448cf200000
start commit:   09ef09b4 drm/vkms: WARN when hrtimer_forward_now fails
git tree:       upstream
final crash:    https://syzkaller.appspot.com/x/report.txt?x=118448cf200000
console output: https://syzkaller.appspot.com/x/log.txt?x=168448cf200000
kernel config:  https://syzkaller.appspot.com/x/.config?x=c1e0e0ec44d1e5ff
dashboard link: https://syzkaller.appspot.com/bug?extid=0871b14ca2e2fb64f6e3
userspace arch: amd64
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1787db8d200000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17fc9883200000

Reported-by: syzbot+0871b14ca2e2fb64f6e3@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 09ef09b4 ("drm/vkms: WARN when hrtimer_forward_now fails")