On 09.11.2017 03:52, Wanpeng Li wrote: > 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 treating the unhotplug pCPU as not using master clock. > > Cc: Paolo Bonzini <[email protected]> > Cc: Radim Krčmář <[email protected]> > Signed-off-by: Wanpeng Li <[email protected]> > --- > 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 <[email protected]> -- Thanks, David / dhildenb
