2017-11-06 04:17-0800, Wanpeng Li:
> From: Wanpeng Li <[email protected]>
>
> watchdog: BUG: soft lockup - CPU#6 stuck for 22s! [qemu-system-x86:10185]
> CPU: 6 PID: 10185 Comm: qemu-system-x86 Tainted: G OE 4.14.0-rc4+ #4
> RIP: 0010:kvm_get_time_scale+0x4e/0xa0 [kvm]
> Call Trace:
> ? get_kvmclock_ns+0xa3/0x140 [kvm]
> get_time_ref_counter+0x5a/0x80 [kvm]
> kvm_hv_process_stimers+0x120/0x5f0 [kvm]
> ? kvm_hv_process_stimers+0x120/0x5f0 [kvm]
> ? preempt_schedule+0x27/0x30
> ? ___preempt_schedule+0x16/0x18
> kvm_arch_vcpu_ioctl_run+0x4b4/0x1690 [kvm]
> ? kvm_arch_vcpu_load+0x47/0x230 [kvm]
> kvm_vcpu_ioctl+0x33a/0x620 [kvm]
> ? kvm_vcpu_ioctl+0x33a/0x620 [kvm]
> ? kvm_vm_ioctl_check_extension_generic+0x3b/0x40 [kvm]
> ? kvm_dev_ioctl+0x279/0x6c0 [kvm]
> do_vfs_ioctl+0xa1/0x5d0
> ? __fget+0x73/0xa0
> SyS_ioctl+0x79/0x90
> entry_SYSCALL_64_fastpath+0x1e/0xa9
>
> This can be reproduced when running kvm-unit-tests/hyperv_stimer.flat and
> cpu-hotplug stress simultaneously. __this_cpu_read(cpu_tsc_khz) returns 0
> (set in kvmclock_cpu_down_prep()) when the pCPU is unhotplug which results
> in kvm_get_time_scale() gets into an infinite loop.
>
> This patch fixes it by skipping to fill the hv_clock when the pCPU is offline.
>
> Cc: Paolo Bonzini <[email protected]>
> Cc: Radim Krčmář <[email protected]>
> Signed-off-by: Wanpeng Li <[email protected]>
> ---
> v1 -> v2:
> * avoid infinite loop
>
> arch/x86/kvm/x86.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 03869eb..d2507c6 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1259,6 +1259,9 @@ static void kvm_get_time_scale(uint64_t scaled_hz, uint64_t base_hz,
> uint64_t tps64;
> uint32_t tps32;
>
> + if (unlikely(base_hz == 0))
> + return;
This is a sensible thing to do and will prevent the loop, but KVM will
still have a minor bug: get_kvmclock_ns() passes uninitialized stack
values with the expectation that kvm_get_time_scale() will set them, but
returning here would result in __pvclock_read_cycles() with random data
and inject timer interrupts early (if not worse).
I think it would be best if kvm_get_time_scale() wasn't executing when
cpu_tsc_khz is 0, by clearing cpu_tsc_khz later and setting earlier;
do you see any problems with moving the CPUHP_AP_X86_KVM_CLK_ONLINE
before CPUHP_AP_ONLINE?
Thanks.
From 1583319037672285676@xxx Mon Nov 06 12:18:20 +0000 2017
X-GM-THRID: 1583276151146767154
X-Gmail-Labels: Inbox,Category Forums,HistoricalUnread