On 09.11.2017 03:52, Wanpeng Li wrote:
> From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
>
> 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 treating the unhotplug pCPU as not using master clock.
>
> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx>
> Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
> ---
> arch/x86/kvm/x86.c | 11 +++++++----
> 1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 03869eb..d61dcce3 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1795,10 +1795,13 @@ u64 get_kvmclock_ns(struct kvm *kvm)
> /* both __this_cpu_read() and rdtsc() should be on the same cpu */
> get_cpu();
>
> - kvm_get_time_scale(NSEC_PER_SEC, __this_cpu_read(cpu_tsc_khz) * 1000LL,
> - &hv_clock.tsc_shift,
> - &hv_clock.tsc_to_system_mul);
> - ret = __pvclock_read_cycles(&hv_clock, rdtsc());
> + if (__this_cpu_read(cpu_tsc_khz)) {
> + kvm_get_time_scale(NSEC_PER_SEC, __this_cpu_read(cpu_tsc_khz) * 1000LL,
> + &hv_clock.tsc_shift,
> + &hv_clock.tsc_to_system_mul);
> + ret = __pvclock_read_cycles(&hv_clock, rdtsc());
> + } else
Can we add a comment like
/* unplugging a physical CPU -> avoid using the master clock */
> + ret = ktime_get_boot_ns() + ka->kvmclock_offset;
>
> put_cpu();
>
>
Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>
--
Thanks,
David / dhildenb
