On 04/11/19 13:25, Wanpeng Li wrote:
> On Mon, 4 Nov 2019 at 20:21, Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
>>
>> On 04/11/19 13:16, Wanpeng Li wrote:
>>>> I don't understand this one, hasn't
>>>>
>>>> WARN_ON_ONCE(!refcount_dec_and_test(&kvm->users_count));
>>>>
>>>> decreased the conut already? With your patch the refcount would then
>>>> underflow.
>>>
>>> r = kvm_arch_init_vm(kvm, type);
>>> if (r)
>>> goto out_err_no_arch_destroy_vm;
>>>
>>> out_err_no_disable:
>>> kvm_arch_destroy_vm(kvm);
>>> WARN_ON_ONCE(!refcount_dec_and_test(&kvm->users_count));
>>> out_err_no_arch_destroy_vm:
>>>
>>> So, if kvm_arch_init_vm() fails, we will not execute
>>> WARN_ON_ONCE(!refcount_dec_and_test(&kvm->users_count));
>>
>> Uuh of course. But I'd rather do the opposite: move the refcount_set
>> earlier so that refcount_dec_and_test can be moved after
>> no_arch_destroy_vm. Moving the refcount_set is not strictly necessary,
>> but avoids the introduction of yet another label.
>>
>> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
>> index e22ff63e5b1a..e7a07132cd7f 100644
>> --- a/virt/kvm/kvm_main.c
>> +++ b/virt/kvm/kvm_main.c
>> @@ -650,6 +650,7 @@ static struct kvm *kvm_create_vm(unsigned long type)
>> if (init_srcu_struct(&kvm->irq_srcu))
>> goto out_err_no_irq_srcu;
>>
>> + refcount_set(&kvm->users_count, 1);
>> for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
>> struct kvm_memslots *slots = kvm_alloc_memslots();
>>
>> @@ -667,7 +668,6 @@ static struct kvm *kvm_create_vm(unsigned long type)
>> goto out_err_no_arch_destroy_vm;
>> }
>>
>> - refcount_set(&kvm->users_count, 1);
>> r = kvm_arch_init_vm(kvm, type);
>> if (r)
>> goto out_err_no_arch_destroy_vm;
>> @@ -696,8 +696,8 @@ static struct kvm *kvm_create_vm(unsigned long type)
>> hardware_disable_all();
>> out_err_no_disable:
>> kvm_arch_destroy_vm(kvm);
>> - WARN_ON_ONCE(!refcount_dec_and_test(&kvm->users_count));
>> out_err_no_arch_destroy_vm:
>> + WARN_ON_ONCE(!refcount_dec_and_test(&kvm->users_count));
>> for (i = 0; i < KVM_NR_BUSES; i++)
>> kfree(kvm_get_bus(kvm, i));
>> for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++)
>
> Good point, I will handle these two patches later.
No problem, I can send v2 after testing.
Paolo
