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WARNING: drivers/gpu/drm/vkms/vkms_crtc.c:97 at vkms_get_vblank_timestamp+0x128/0x16c drivers/gpu/drm/vkms/vkms_crtc.c:110, CPU#1: syz.0.1161/5833
Modules linked in:
CPU: 1 UID: 0 PID: 5833 Comm: syz.0.1161 Not tainted syzkaller #0 PREEMPT 
Hardware name: linux,dummy-virt (DT)
pstate: 60000005 (nZCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : vkms_get_vblank_timestamp+0x128/0x16c drivers/gpu/drm/vkms/vkms_crtc.c:97
lr : vkms_get_vblank_timestamp+0x20/0x16c drivers/gpu/drm/vkms/vkms_crtc.c:88
sp : ffff80008f6472f0
x29: ffff80008f6472f0 x28: ffff000014271000 x27: 0000000000000003
x26: ffff00000f70c080 x25: 0000000000000001 x24: 1fffe00001ef0a38
x23: ffff800085be1ba0 x22: ffff80008f6474c0 x21: 000000c25d30d500
x20: ffff00000f70c080 x19: ffff00000f785080 x18: 0000000000000002
x17: ffff00001428b908 x16: ffff00006a068504 x15: ffff800080b19ce8
x14: ffff80008191a978 x13: 0000000000000000 x12: ffff80008e9d9000
x11: 1fffe00002b3d822 x10: ffff600002b3d822 x9 : dfff800000000000
x8 : 0000000041b58ab3 x7 : ffff700011ec8e6e x6 : dfff800000000000
x5 : 0000000000000000 x4 : 1fffe00001ef0a4a x3 : 0000000000000000
x2 : 1fffe00001ef0a35 x1 : 0000000000000000 x0 : 000000c25d30d500
Call trace:
 vkms_get_vblank_timestamp+0x128/0x16c drivers/gpu/drm/vkms/vkms_crtc.c:110 (P)
 drm_crtc_get_last_vbltimestamp+0x140/0x184 drivers/gpu/drm/drm_vblank.c:879
 drm_crtc_next_vblank_start+0x11c/0x244 drivers/gpu/drm/drm_vblank.c:1013
 set_fence_deadline drivers/gpu/drm/drm_atomic_helper.c:1718 [inline]
 drm_atomic_helper_wait_for_fences+0x184/0x614 drivers/gpu/drm/drm_atomic_helper.c:1765
 drm_atomic_helper_commit+0x170/0x2b4 drivers/gpu/drm/drm_atomic_helper.c:2194
 drm_atomic_commit+0x18c/0x23c drivers/gpu/drm/drm_atomic.c:1577
 drm_client_modeset_commit_atomic+0x4a4/0x5f8 drivers/gpu/drm/drm_client_modeset.c:1103
 drm_client_modeset_commit_locked+0x108/0x3f8 drivers/gpu/drm/drm_client_modeset.c:1206
 pan_display_atomic drivers/gpu/drm/drm_fb_helper.c:1381 [inline]
 drm_fb_helper_pan_display+0x260/0x844 drivers/gpu/drm/drm_fb_helper.c:1441
 fb_pan_display+0x1d0/0x5f8 drivers/video/fbdev/core/fbmem.c:193
 bit_update_start+0x40/0x198 drivers/video/fbdev/core/bitblit.c:405
 fbcon_modechanged+0x42c/0x554 drivers/video/fbdev/core/fbcon.c:2708
 fbcon_set_all_vcs+0x29c/0x364 drivers/video/fbdev/core/fbcon.c:2748
 fbcon_update_vcs+0x18/0x34 drivers/video/fbdev/core/fbcon.c:2755
 do_fb_ioctl+0x6c0/0x80c drivers/video/fbdev/core/fb_chrdev.c:92
 fb_ioctl+0xcc/0x140 drivers/video/fbdev/core/fb_chrdev.c:169
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl fs/ioctl.c:583 [inline]
 __arm64_sys_ioctl+0x124/0x1a4 fs/ioctl.c:583
 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
 invoke_syscall+0x6c/0x258 arch/arm64/kernel/syscall.c:49
 el0_svc_common.constprop.0+0xac/0x230 arch/arm64/kernel/syscall.c:132
 do_el0_svc+0x40/0x58 arch/arm64/kernel/syscall.c:151
 el0_svc+0x54/0x2b0 arch/arm64/kernel/entry-common.c:724
 el0t_64_sync_handler+0xa0/0xe4 arch/arm64/kernel/entry-common.c:743
 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596
irq event stamp: 1636
hardirqs last  enabled at (1635): [<ffff800085532bb8>] irqentry_exit+0x190/0x474 kernel/entry/common.c:219
hardirqs last disabled at (1636): [<ffff80008552bdbc>] el1_brk64+0x20/0x54 arch/arm64/kernel/entry-common.c:412
softirqs last  enabled at (1032): [<ffff8000801c6e98>] softirq_handle_end kernel/softirq.c:468 [inline]
softirqs last  enabled at (1032): [<ffff8000801c6e98>] handle_softirqs+0x88c/0xdb4 kernel/softirq.c:650
softirqs last disabled at (1025): [<ffff8000800107dc>] __do_softirq+0x14/0x20 kernel/softirq.c:656
---[ end trace 0000000000000000 ]---