From c09664bb44184b3846e8c5254db4eae4b932682a Mon Sep 17 00:00:00 2001 From: Marcelo Tosatti Date: Mon, 18 Mar 2013 13:54:32 -0300 Subject: [PATCH] KVM: x86: fix deadlock in clock-in-progress request handling There is a deadlock in pvclock handling: cpu0: cpu1: kvm_gen_update_masterclock() kvm_guest_time_update() spin_lock(pvclock_gtod_sync_lock) local_irq_save(flags) spin_lock(pvclock_gtod_sync_lock) kvm_make_mclock_inprogress_request(kvm) make_all_cpus_request() smp_call_function_many() Now if smp_call_function_many() called by cpu0 tries to call function on cpu1 there will be a deadlock. Fix by moving pvclock_gtod_sync_lock protected section outside irq disabled section. Analyzed by Gleb Natapov Acked-by: Gleb Natapov Reported-and-Tested-by: Yongjie Ren Signed-off-by: Marcelo Tosatti --- arch/x86/kvm/x86.c | 18 +++++++++--------- 1 file changed, 9 insertions(+), 9 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index f71500af1f8..f7c850b3691 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -1416,15 +1416,6 @@ static int kvm_guest_time_update(struct kvm_vcpu *v) kernel_ns = 0; host_tsc = 0; - /* Keep irq disabled to prevent changes to the clock */ - local_irq_save(flags); - this_tsc_khz = __get_cpu_var(cpu_tsc_khz); - if (unlikely(this_tsc_khz == 0)) { - local_irq_restore(flags); - kvm_make_request(KVM_REQ_CLOCK_UPDATE, v); - return 1; - } - /* * If the host uses TSC clock, then passthrough TSC as stable * to the guest. @@ -1436,6 +1427,15 @@ static int kvm_guest_time_update(struct kvm_vcpu *v) kernel_ns = ka->master_kernel_ns; } spin_unlock(&ka->pvclock_gtod_sync_lock); + + /* Keep irq disabled to prevent changes to the clock */ + local_irq_save(flags); + this_tsc_khz = __get_cpu_var(cpu_tsc_khz); + if (unlikely(this_tsc_khz == 0)) { + local_irq_restore(flags); + kvm_make_request(KVM_REQ_CLOCK_UPDATE, v); + return 1; + } if (!use_master_clock) { host_tsc = native_read_tsc(); kernel_ns = get_kernel_ns(); -- 2.41.0