On 2020/05/26 2:00, Daniel Vetter wrote: > Forgot to add: I did run this quickly with vkms as secondary output. > Good fireworks show, but there's an entire army of additional splats > after the first one. The WARN_ON you're removing is only the > messenger, the real bug is probably one of the later backtraces. Or at > least points more clearly at the real bug. > -Daniel > >> >> Debug printk() patch shows that hrtimer_forward_now() can return larger than 1. >> What is the reason you are expecting hrtimer_forward_now() to always return 1 ? >> >>> >>> If the vkms driver is loaded, and there's nothing else going on, then what >>> I expect to happen is that this virtual hw is entirely off. And in that >>> case, the vblank ioctl should be rejected outright. So there's definitely >>> something fishy going on to begin with. >>> >>> If otoh the virtual hw is somehow on (maybe fbcon gets loaded, no idea), >>> then the vblank wait shouldn't just blow up like this. I see. Another debug printk() patch ( https://syzkaller.appspot.com/text?tag=Patch&x=135f254a100000 ) found that [ 86.613767][ T7837] [drm:drm_stub_open] [ 86.621592][ T7837] [drm:drm_open] pid = 7837, minor = 1 [ 86.651632][ T7837] [drm:drm_ioctl] pid=7837, dev=0xe201, auth=1, DRM_IOCTL_WAIT_VBLANK [ 86.663391][ T7837] [drm:drm_calc_timestamping_constants] *ERROR* crtc 32: Can't calculate constants, dotclock = 0! [ 86.679151][ T7837] [drm:drm_calc_timestamping_constants] crtc 32: hwmode: htotal 0, vtotal 0, vdisplay 0 [ 86.688865][ T7837] [drm:drm_calc_timestamping_constants] crtc 32: clock 0 kHz framedur 0 linedur 0 [ 86.688899][ T7837] Starting out->vblank_hrtimer : out->period_ns=0 vblank->framedur_ns=0 [ 86.689348][ T7837] [drm:drm_vblank_enable] enabling vblank on crtc 0, ret: 0 [ 86.706883][ T7837] [drm:drm_update_vblank_count] updating vblank count on crtc 0: current=0, diff=0, hw=0 hw_last=0 [ 86.706962][ C1] now=86714983667 interval=0 ret_overrun=17693375 hrtimer_start(&out->vblank_hrtimer, 0, HRTIMER_MODE_REL) from vkms_enable_vblank() is causing immediate vkms_vblank_simulate() callback. The reason of vblank->framedur_ns == 0 is that drm_calc_timestamping_constants() fails to calculate framedur_ns (which is 0 by default) due to mode->crtc_clock <= 0. Thus, somehow initializing mode->crtc_clock > 0 might be able to solve this problem. By the way, if you have an environment that can reproduce this problem, you can test with debug printk() patch above applied. _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
