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; + tps64 = base_hz; scaled64 = scaled_hz; while (tps64 > scaled64*2 || tps64 & 0xffffffff00000000ULL) { -- 2.7.4
