Re: INFO: rcu detected stall in vcpu_enter_guest

[Dmitry Vyukov]

On Sun, May 6, 2018 at 11:31 AM, syzbot
<syzbot+f58b8603b48434ef07d3@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit:    625e2001e99e Merge tag 'for-linus-4.17-rc4-tag' of git://g..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=16ecc697800000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=5a1dc06635c10d27
> dashboard link: https://syzkaller.appspot.com/bug?extid=f58b8603b48434ef07d3
> compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
>
> Unfortunately, I don't have any reproducer for this crash yet.

>From the log the program that triggered this seems to be:

2018/05/05 01:26:03 executing program 3:
sched_setattr(0x0, &(0x7f0000000080)={0x0, 0x2, 0x0, 0x0, 0x3}, 0x0)
r0 = openat$kvm(0xffffffffffffff9c, &(0x7f0000000380)='/dev/kvm\x00', 0x0, 0x0)
r1 = ioctl$KVM_CREATE_VM(r0, 0xae01, 0x0)
r2 = ioctl$KVM_CREATE_VCPU(r1, 0xae41, 0x0)
syz_kvm_setup_cpu$x86(r1, r2, &(0x7f0000000000/0x18000)=nil,
&(0x7f0000000280)=[@text64={0x40,
&(0x7f0000000500)="0f0866b8ed008ec066ba4000b000eed2a807000000410f01cab98e0b0000b862000000ba000000000f30b90b0800000f320fc72a8f2a60128f00000000003000000fc7aa00100000",
0x48}], 0x1, 0x5d, &(0x7f0000000580), 0x0)
ioctl$KVM_SET_DEBUGREGS(0xffffffffffffffff, 0x4080aea2,
&(0x7f0000000000)={[0x0, 0x0, 0x4000]})
ioctl$KVM_RUN(r2, 0xae80, 0x0)
ioctl$KVM_GET_MP_STATE(r2, 0x8004ae98, &(0x7f0000000100))
ioctl$KVM_RUN(r2, 0xae80, 0x0)
ioctl$KVM_SET_GUEST_DEBUG(0xffffffffffffffff, 0x4048ae9b, &(0x7f0000000080))

Wonder if this is guest-triggerable too...



> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+f58b8603b48434ef07d3@xxxxxxxxxxxxxxxxxxxxxxxxx
>
> INFO: rcu_sched detected stalls on CPUs/tasks:
>         (detected by 1, t=125002 jiffies, g=73789, c=73788, q=844)
> All QSes seen, last rcu_sched kthread activity 125002
> (4295195361-4295070359), jiffies_till_next_fqs=3, root ->qsmask 0x0
> syz-executor3   R  running task    23000 27493  11463 0x00000000
> Call Trace:
>  <IRQ>
>  sched_show_task.cold.86+0x27a/0x301 kernel/sched/core.c:5325
>  print_other_cpu_stall.cold.79+0x92f/0x9d2 kernel/rcu/tree.c:1481
>  check_cpu_stall.isra.61+0x706/0xf50 kernel/rcu/tree.c:1599
>  __rcu_pending kernel/rcu/tree.c:3356 [inline]
>  rcu_pending kernel/rcu/tree.c:3401 [inline]
>  rcu_check_callbacks+0x21b/0xad0 kernel/rcu/tree.c:2763
>  update_process_times+0x2d/0x70 kernel/time/timer.c:1636
>  tick_sched_handle+0x9f/0x180 kernel/time/tick-sched.c:164
>  tick_sched_timer+0x45/0x130 kernel/time/tick-sched.c:1274
>  __run_hrtimer kernel/time/hrtimer.c:1398 [inline]
>  __hrtimer_run_queues+0x3e3/0x10a0 kernel/time/hrtimer.c:1460
>  hrtimer_interrupt+0x2f3/0x750 kernel/time/hrtimer.c:1518
>  local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1025 [inline]
>  smp_apic_timer_interrupt+0x15d/0x710 arch/x86/kernel/apic/apic.c:1050
>  apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:863
>  </IRQ>
> RIP: 0010:vmx_handle_external_intr+0x1b4/0x220 arch/x86/kvm/vmx.c:9459
> RSP: 0018:ffff8801bb297508 EFLAGS: 00000086 ORIG_RAX: ffffffffffffff13
> RAX: ffffffff87801530 RBX: fffffe0000000ec0 RCX: 0000000000000000
> RDX: ffff8801bb297508 RSI: 0000000000000001 RDI: fffffe0000000ec8
> RBP: ffff8801bb297520 R08: ffff8801d93c6780 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000000 R12: 0000000087800000
> R13: 0000000000001530 R14: 0000000000000000 R15: 0000000000000000
>  vcpu_enter_guest+0x1121/0x6060 arch/x86/kvm/x86.c:7470
>  vcpu_run arch/x86/kvm/x86.c:7559 [inline]
>  kvm_arch_vcpu_ioctl_run+0x33e/0x1690 arch/x86/kvm/x86.c:7736
>  kvm_vcpu_ioctl+0x79d/0x12e0 arch/x86/kvm/../../../virt/kvm/kvm_main.c:2560
>  vfs_ioctl fs/ioctl.c:46 [inline]
>  file_ioctl fs/ioctl.c:500 [inline]
>  do_vfs_ioctl+0x1cf/0x16a0 fs/ioctl.c:684
>  ksys_ioctl+0xa9/0xd0 fs/ioctl.c:701
>  __do_sys_ioctl fs/ioctl.c:708 [inline]
>  __se_sys_ioctl fs/ioctl.c:706 [inline]
>  __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:706
>  do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x455979
> RSP: 002b:00007f9c60b4bc68 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> RAX: ffffffffffffffda RBX: 00007f9c60b4c6d4 RCX: 0000000000455979
> RDX: 0000000000000000 RSI: 000000000000ae80 RDI: 0000000000000015
> RBP: 000000000072bea0 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
> R13: 000000000000027e R14: 00000000006f7c70 R15: 0000000000000000
> rcu_sched kthread starved for 125002 jiffies! g73789 c73788 f0x2
> RCU_GP_WAIT_FQS(3) ->state=0x0 ->cpu=0
> RCU grace-period kthread stack dump:
> rcu_sched       R  running task    23592     9      2 0x80000000
> Call Trace:
>  context_switch kernel/sched/core.c:2848 [inline]
>  __schedule+0x801/0x1e30 kernel/sched/core.c:3490
>  schedule+0xef/0x430 kernel/sched/core.c:3549
>  schedule_timeout+0x138/0x240 kernel/time/timer.c:1801
>  rcu_gp_kthread+0x6b5/0x1940 kernel/rcu/tree.c:2231
>  kthread+0x345/0x410 kernel/kthread.c:238
>  ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:412
>
>
> ---
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