Re: KVM host kernel hang

[Avi Kivity <avi@redhat.com>]

Alexander Graf wrote:
> Avi Kivity wrote:
>   
>> Alexander Graf wrote:
>>     
>>> I have CONFIG_LOCKDEP_SUPPORT=y. How do I make it detect that it's
>>> actually locking itself up?
>>> Btw: The issue seems to be easily reproducible :-)
>>>       
>> Perhaps CONFIG_PROVE_LOCKING and CONFIG_LOCKDEP.  _SUPPORT just
>> indicates the arch can do it if you want, IIUC.
>>     
>
> I just added some debug #define's to show me where exactly things break.
>
>
> Jan  7 14:34:46 linux-dp8n kernel: 2149: Grabbing lock {
> Jan  7 14:34:46 linux-dp8n kernel: 1908: Grabbing lock {
>
>    2145 mmio:
>    2146         /*
>    2147          * Is this MMIO handled locally?
>    2148          */
>    2149         mutex_lock(&vcpu->kvm->lock);
>    2150         mmio_dev = vcpu_find_mmio_dev(vcpu, gpa, bytes, 0);
>    2151         if (mmio_dev) {
>    2152                 kvm_iodevice_read(mmio_dev, gpa, bytes, val);
>    2153                 mutex_unlock(&vcpu->kvm->lock);
>    2154                 return X86EMUL_CONTINUE;
>    2155         }
>    2156         mutex_unlock(&vcpu->kvm->lock);
>
>   

The lock was lost here.  But how?

>    1901         case KVM_IRQ_LINE: {
>    1902                 struct kvm_irq_level irq_event;
>    1903
>    1904                 r = -EFAULT;
>    1905                 if (copy_from_user(&irq_event, argp, sizeof
> irq_event))
>    1906                         goto out;
>    1907                 if (irqchip_in_kernel(kvm)) {
>    1908                         mutex_lock(&kvm->lock);
>    1909                         kvm_set_irq(kvm,
> KVM_USERSPACE_IRQ_SOURCE_ID,
>    1910                                     irq_event.irq, irq_event.level);
>    1911                         mutex_unlock(&kvm->lock);
>    1912                         r = 0;
>    1913                 }
>    1914                 break;
>    1915         }
>
>   
This is your hung iothread trying to inject an interrupt.  It's waiting 
for the lost lock.

I suggest enabling all the lock debug magic you can find in kconfig.

-- 
error compiling committee.c: too many arguments to function