[syzbot] upstream boot error: WARNING in vkms_vblank_simulate

Dmitry Vyukov dvyukov at google.com
Fri Mar 12 16:10:43 UTC 2021 

On Fri, Mar 12, 2021 at 3:22 PM Daniel Vetter <daniel at ffwll.ch> wrote:
>
> On Fri, Mar 12, 2021 at 11:46:27AM +0100, Dmitry Vyukov wrote:
> > On Fri, Mar 12, 2021 at 11:26 AM syzbot
> > <syzbot+333bd014262fd5d0a418 at syzkaller.appspotmail.com> wrote:
> > >
> > > Hello,
> > >
> > > syzbot found the following issue on:
> > >
> > > HEAD commit:    f78d76e7 Merge tag 'drm-fixes-2021-03-12-1' of git://anong..
> > > git tree:       upstream
> > > console output: https://syzkaller.appspot.com/x/log.txt?x=11c16ba2d00000
> > > kernel config:  https://syzkaller.appspot.com/x/.config?x=dc02c6afcb046874
> > > dashboard link: https://syzkaller.appspot.com/bug?extid=333bd014262fd5d0a418
> > > userspace arch: arm
> > >
> > > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > > Reported-by: syzbot+333bd014262fd5d0a418 at syzkaller.appspotmail.com
> >
> > This WARNING seems to be happening just randomly.
> > It was already reported as:
> >
> > #syz dup: WARNING in vkms_vblank_simulate (2)
> > https://syzkaller.appspot.com/bug?id=9b10491371879700d6a21c15684c2232ff015084
> >
> > It now has whooping 48589 crashes and also crashes slow qemu tcg instances.
>
> Yeah your box is too slow. We're trying to simulate hw here, which means
> if we can process less than 1 hrtimer per vblank (standard every 16ms)
> then we scream, because things go very wrong with the simulated hw. And
> the hrtimer is really not that big, all the expensive processing is pushed
> to worker, where we have code to handle if it falls back too much.
>
> So either patch this out or make the code robust against a kernel that
> somehow can't process a single hrtimer every 16ms.
> -Daniel

Majority of these happen on the latest Intel CPUs. If that's not fast,
then I don't know what' fast :)
WARNING must not be used for timing-triggerable conditions. pr_warn is
more appropriate here. I assume the call stack and the rest of the
info that WARNING prints is completely useless, it's only the binary
condition, right.


> > > ------------[ cut here ]------------
> > > WARNING: CPU: 0 PID: 0 at drivers/gpu/drm/vkms/vkms_crtc.c:21 vkms_vblank_simulate+0x26c/0x2f4 drivers/gpu/drm/vkms/vkms_crtc.c:41
> > > Modules linked in:
> > > CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.12.0-rc2-syzkaller-00338-gf78d76e72a46 #0
> > > Hardware name: linux,dummy-virt (DT)
> > > pstate: 20000085 (nzCv daIf -PAN -UAO -TCO BTYPE=--)
> > > pc : vkms_vblank_simulate+0x26c/0x2f4 drivers/gpu/drm/vkms/vkms_crtc.c:21
> > > lr : hrtimer_forward_now include/linux/hrtimer.h:510 [inline]
> > > lr : vkms_vblank_simulate+0x90/0x2f4 drivers/gpu/drm/vkms/vkms_crtc.c:19
> > > sp : ffff00006a693cd0
> > > x29: ffff00006a693cd0 x28: ffff00000c9d1e58
> > > x27: dfff800000000000 x26: ffff00006a67f540
> > > x25: 1fffe0000d4cfeb1 x24: 1fffe0000d4cfeaa
> > > x23: ffff00000c9d0d30 x22: 0000000000fe4c00
> > > x21: ffff00006a67f540 x20: ffff00000c9d0e58
> > > x19: ffff00000c9d1e58 x18: ffff00006a6a1b48
> > > x17: 1fffe00001952345 x16: 0000000000000000
> > > x15: ffff8000197bf810 x14: 1fffe0000d4d2750
> > > x13: 0000000000000001 x12: 0000000000000033
> > > x11: 1ffff00002fb4936 x10: 0000000000000007
> > > x9 : 1ffff00002fb4943 x8 : ffff800017d14c00
> > > x7 : 00000000f1f1f1f1 x6 : dfff800000000000
> > > x5 : 7fffffffffffffff x4 : 00000008e44f6b90
> > > x3 : 00000008e54db790 x2 : 00000008e44f6b90
> > > x1 : 00000008e54db790 x0 : 0000000000000002
> > > Call trace:
> > >  vkms_vblank_simulate+0x26c/0x2f4 drivers/gpu/drm/vkms/vkms_crtc.c:41
> > >  __run_hrtimer kernel/time/hrtimer.c:1519 [inline]
> > >  __hrtimer_run_queues+0x590/0xe40 kernel/time/hrtimer.c:1583
> > >  hrtimer_interrupt+0x2d4/0x810 kernel/time/hrtimer.c:1645
> > >  timer_handler drivers/clocksource/arm_arch_timer.c:647 [inline]
> > >  arch_timer_handler_phys+0x4c/0x70 drivers/clocksource/arm_arch_timer.c:665
> > >  handle_percpu_devid_irq+0x19c/0x330 kernel/irq/chip.c:930
> > >  generic_handle_irq_desc include/linux/irqdesc.h:158 [inline]
> > >  generic_handle_irq kernel/irq/irqdesc.c:652 [inline]
> > >  __handle_domain_irq+0x11c/0x1f0 kernel/irq/irqdesc.c:689
> > >  handle_domain_irq include/linux/irqdesc.h:176 [inline]
> > >  gic_handle_irq+0x5c/0x1b0 drivers/irqchip/irq-gic.c:370
> > >  el1_irq+0xb4/0x180 arch/arm64/kernel/entry.S:669
> > >  arch_local_irq_restore arch/arm64/include/asm/irqflags.h:124 [inline]
> > >  queue_work_on+0x74/0x110 kernel/workqueue.c:1528
> > >  queue_work include/linux/workqueue.h:507 [inline]
> > >  cursor_timer_handler+0x64/0x100 drivers/video/fbdev/core/fbcon.c:397
> > >  call_timer_fn+0x1d4/0x9c4 kernel/time/timer.c:1431
> > >  expire_timers kernel/time/timer.c:1476 [inline]
> > >  __run_timers.part.0+0x530/0xa00 kernel/time/timer.c:1745
> > >  __run_timers kernel/time/timer.c:1726 [inline]
> > >  run_timer_softirq+0xa4/0x1a0 kernel/time/timer.c:1758
> > >  _stext+0x2b4/0x1084
> > >  do_softirq_own_stack include/asm-generic/softirq_stack.h:10 [inline]
> > >  invoke_softirq kernel/softirq.c:228 [inline]
> > >  __irq_exit_rcu+0x46c/0x510 kernel/softirq.c:422
> > >  irq_exit+0x14/0x84 kernel/softirq.c:446
> > >  __handle_domain_irq+0x120/0x1f0 kernel/irq/irqdesc.c:692
> > >  handle_domain_irq include/linux/irqdesc.h:176 [inline]
> > >  gic_handle_irq+0x5c/0x1b0 drivers/irqchip/irq-gic.c:370
> > >  el1_irq+0xb4/0x180 arch/arm64/kernel/entry.S:669
> > >  arch_local_irq_enable+0xc/0x14 arch/arm64/include/asm/irqflags.h:37
> > >  default_idle_call+0x64/0xf4 kernel/sched/idle.c:112
> > >  cpuidle_idle_call kernel/sched/idle.c:194 [inline]
> > >  do_idle+0x38c/0x4ec kernel/sched/idle.c:300
> > >  cpu_startup_entry+0x28/0x80 kernel/sched/idle.c:397
> > >  rest_init+0x1d0/0x2cc init/main.c:721
> > >  arch_call_rest_init+0x10/0x1c
> > >  start_kernel+0x3b0/0x3e8 init/main.c:1064
> > >  0x0
> > >
> > >
> > > ---
> > > This report is generated by a bot. It may contain errors.
> > > See https://goo.gl/tpsmEJ for more information about syzbot.
> > > syzbot engineers can be reached at syzkaller at googlegroups.com.
> > >
> > > syzbot will keep track of this issue. See:
> > > https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> > >
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>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch

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