WARNING in vkms_vblank_simulate

[syzbot <syzbot+0871b14ca2e2fb64f6e3@syzkaller.appspotmail.com>]

Hello,

syzbot found the following crash on:

HEAD commit:    d4104460aec1 Add linux-next specific files for 20190211
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=10e74624c00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=c8a112d3b0d6719b
dashboard link: https://syzkaller.appspot.com/bug?extid=0871b14ca2e2fb64f6e3
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12d8e6b0c00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15c6c804c00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+0871b14ca2e2fb64f6e3@syzkaller.appspotmail.com

WARNING: CPU: 1 PID: 7773 at drivers/gpu/drm/vkms/vkms_crtc.c:40  
vkms_vblank_simulate+0x262/0x2c0 drivers/gpu/drm/vkms/vkms_crtc.c:40
Kernel panic - not syncing: panic_on_warn set ...
CPU: 1 PID: 7773 Comm: syz-executor184 Not tainted 5.0.0-rc5-next-20190211  
#32
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
  <IRQ>
  __dump_stack lib/dump_stack.c:77 [inline]
  dump_stack+0x172/0x1f0 lib/dump_stack.c:113
  panic+0x2cb/0x65c kernel/panic.c:214
  __warn.cold+0x20/0x45 kernel/panic.c:571
  report_bug+0x263/0x2b0 lib/bug.c:186
  fixup_bug arch/x86/kernel/traps.c:178 [inline]
  fixup_bug arch/x86/kernel/traps.c:173 [inline]
  do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:271
  do_invalid_op+0x37/0x50 arch/x86/kernel/traps.c:290
  invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:973
RIP: 0010:vkms_vblank_simulate+0x262/0x2c0  
drivers/gpu/drm/vkms/vkms_crtc.c:40
Code: c7 c7 a0 bc bd 87 e8 5d 3d bb ff e9 2c fe ff ff e8 13 0e 9b fd 48 8b  
45 d0 49 89 86 40 02 00 00 e9 7a ff ff ff e8 fe 0d 9b fd <0f> 0b e9 f4 fe  
ff ff e8 b2 d2 d2 fd e9 34 fe ff ff e8 08 d3 d2 fd
RSP: 0018:ffff8880ae907dd8 EFLAGS: 00010006
RAX: ffff888098fb2480 RBX: ffff8880ae925d80 RCX: ffffffff83d53af3
RDX: 0000000000010000 RSI: ffffffff83d53c02 RDI: 0000000000000007
RBP: ffff8880ae907e08 R08: ffff888098fb2480 R09: ffffffff899a5048
R10: ffffffff899a5050 R11: 0000000000000001 R12: 0000000000055ce8
R13: ffff8881d09a99c0 R14: 0000000000000000 R15: ffff8881d09a8e98
  __run_hrtimer kernel/time/hrtimer.c:1389 [inline]
  __hrtimer_run_queues+0x33e/0xde0 kernel/time/hrtimer.c:1451
  hrtimer_interrupt+0x314/0x770 kernel/time/hrtimer.c:1509
  local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1035 [inline]
  smp_apic_timer_interrupt+0x120/0x570 arch/x86/kernel/apic/apic.c:1060
  apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:807
  </IRQ>
RIP: 0010:arch_local_irq_restore arch/x86/include/asm/paravirt.h:767  
[inline]
RIP: 0010:__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:160  
[inline]
RIP: 0010:_raw_spin_unlock_irqrestore+0x95/0xe0  
kernel/locking/spinlock.c:184
Code: 48 c7 c0 f0 89 92 88 48 ba 00 00 00 00 00 fc ff df 48 c1 e8 03 80 3c  
10 00 75 39 48 83 3d c2 86 8b 01 00 74 24 48 89 df 57 9d <0f> 1f 44 00 00  
bf 01 00 00 00 e8 cc c2 46 fa 65 8b 05 45 ea fa 78
RSP: 0018:ffff88801de8f938 EFLAGS: 00000286 ORIG_RAX: ffffffffffffff13
RAX: 1ffffffff112513e RBX: 0000000000000286 RCX: 0000000000000000
RDX: dffffc0000000000 RSI: 0000000000000006 RDI: 0000000000000286
RBP: ffff88801de8f948 R08: ffff888098fb2480 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffff8881d09a8430
R13: 0000000000000000 R14: ffff8881d09a8430 R15: ffff888066cda608
  spin_unlock_irqrestore include/linux/spinlock.h:384 [inline]
  drm_vblank_get+0x150/0x1e0 drivers/gpu/drm/drm_vblank.c:1006
  drm_wait_vblank_ioctl+0x4f8/0x17a0 drivers/gpu/drm/drm_vblank.c:1627
  drm_ioctl_kernel+0x23e/0x2e0 drivers/gpu/drm/drm_ioctl.c:758
  drm_ioctl+0x545/0xa50 drivers/gpu/drm/drm_ioctl.c:858
  vfs_ioctl fs/ioctl.c:46 [inline]
  file_ioctl fs/ioctl.c:509 [inline]
  do_vfs_ioctl+0xd6e/0x1390 fs/ioctl.c:696
  ksys_ioctl+0xab/0xd0 fs/ioctl.c:713
  __do_sys_ioctl fs/ioctl.c:720 [inline]
  __se_sys_ioctl fs/ioctl.c:718 [inline]
  __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
  do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
  entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x443ca9
Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 48 89 f8 48 89 f7  
48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff  
ff 0f 83 7b d8 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fff8472a0d8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000004002e0 RCX: 0000000000443ca9
RDX: 0000000020000000 RSI: 00000000c018643a RDI: 0000000000000003
RBP: 00000000006ce018 R08: 0000000000000000 R09: 00000000004002e0
R10: 000000000000000f R11: 0000000000000246 R12: 00000000004019b0
R13: 0000000000401a40 R14: 0000000000000000 R15: 0000000000000000
Kernel Offset: disabled
Rebooting in 86400 seconds..


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