On Mon, Mar 18, 2013 at 01:54:32PM -0300, Marcelo Tosatti wrote:
>
> 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 <gleb@xxxxxxxxxx>
> Reported-and-Tested-by: Yongjie Ren <yongjie.ren@xxxxxxxxx>
> Signed-off-by: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
>
Acked-by: Gleb Natapov <gleb@xxxxxxxxxx>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index f71500a..f7c850b 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();
--
Gleb.
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
