Hi, I am reporting a WARNING triggered by a syzkaller reproducer in the DRM/VKMS path on Linux 7.2-rc3.
The warning is emitted from drm_crtc_wait_one_vblank() because waiting for one vblank on CRTC 0 times out: faux_driver vkms: [drm] ERROR [CRTC:45] flip_done timed out faux_driver vkms: [drm] vblank wait timed out on crtc 0 WARNING: drivers/gpu/drm/drm_vblank.c:1329 at drm_crtc_wait_one_vblank+0x2f3/0x560 This looks like a VKMS / DRM fb-helper / DRM vblank interaction issue. The reproducer opens DRM devices, queries KMS resources and plane resources, and then issues DRM_IOCTL_MODE_SETCRTC with the returned CRTC/plane identifiers. After that, drm_fb_helper_damage_work() runs from the events workqueue and waits for a vblank through drm_client_modeset_wait_for_vblank(), but no vblank is observed before the timeout. Since panic_on_warn is enabled, the warning is converted into a kernel panic. A similar vblank timeout warning in drm_crtc_wait_one_vblank() may have been reported before, but I can still reproduce this issue on Linux 7.2-rc3. Reproducer: syz reproducer: https://pastebin.com/raw/HeCMiVFR console output: https://pastebin.com/raw/Y5CinzRS kernel config: https://pastebin.com/raw/Lqbb3fQn Kernel: HEAD commit: 1137d8b5df06137fb49513cc923b3b24d94cb809 git tree: torvalds/linux kernel version: 7.2.0-rc3 #1 PREEMPT(full) (QEMU Ubuntu 24.10) Crash log: [ 78.750312][T10019] faux_driver vkms: [drm] ERROR [CRTC:45] flip_done timed out [ 79.792561][ T793] faux_driver vkms: [drm] vblank wait timed out on crtc 0 [ 79.796488][ T793] WARNING: drivers/gpu/drm/drm_vblank.c:1329 at drm_crtc_wait_one_vblank+0x2f3/0x560, CPU#1: kworker/1:2/793 [ 79.813855][ T793] Workqueue: events drm_fb_helper_damage_work [ 79.849602][ T793] <TASK> [ 79.855848][ T793] drm_client_modeset_wait_for_vblank+0xf1/0x130 [ 79.857114][ T793] drm_fb_helper_damage_work+0x2e1/0xae0 [ 79.860522][ T793] process_scheduled_works+0x5ed/0x1c90 [ 79.864431][ T793] worker_thread+0x5be/0xd20 [ 79.866835][ T793] kthread+0x404/0x530 [ 79.867639][ T793] ret_from_fork+0x7c5/0xde0 [ 79.872873][ T793] ret_from_fork_asm+0x1a/0x30 [ 79.873717][ T793] </TASK> [ 79.874264][ T793] Kernel panic - not syncing: kernel: panic_on_warn set ... Thanks
