Re: [PATCH] KVM: fix spin_lock_init order on x86

[Eric Dumazet]

On Mon, 2016-03-21 at 10:24 +0100, Paolo Bonzini wrote:
> kvm_arch_init_vm is now using mmu_lock, causing lockdep to
> complain:
...
> 
> Reported-by: Borislav Petkov <b...@alien8.de>
> Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
> ---
>  virt/kvm/kvm_main.c | 20 ++++++++++----------
>  1 file changed, 10 insertions(+), 10 deletions(-)
> 
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 7ba1d10ffed2..cb45b86a1c48 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -536,6 +536,16 @@ static struct kvm *kvm_create_vm(unsigned long type)
>       if (!kvm)
>               return ERR_PTR(-ENOMEM);
>  
> +     spin_lock_init(&kvm->mmu_lock);
> +     kvm->mm = current->mm;
> +     atomic_inc(&kvm->mm->mm_count);

current->mm->mm_count is incremented here.

> +     kvm_eventfd_init(kvm);
> +     mutex_init(&kvm->lock);
> +     mutex_init(&kvm->irq_lock);
> +     mutex_init(&kvm->slots_lock);
> +     atomic_set(&kvm->users_count, 1);
> +     INIT_LIST_HEAD(&kvm->devices);
> +
>       r = kvm_arch_init_vm(kvm, type);
>       if (r)
>               goto out_err_no_disable;


But out_err_no_disable wont decrement it in case of an error.

This is not clear to me where the cleanup is done ?

> @@ -568,16 +578,6 @@ static struct kvm *kvm_create_vm(unsigned long type)
>                       goto out_err;
>       }
>  
> -     spin_lock_init(&kvm->mmu_lock);
> -     kvm->mm = current->mm;
> -     atomic_inc(&kvm->mm->mm_count);
> -     kvm_eventfd_init(kvm);
> -     mutex_init(&kvm->lock);
> -     mutex_init(&kvm->irq_lock);
> -     mutex_init(&kvm->slots_lock);
> -     atomic_set(&kvm->users_count, 1);
> -     INIT_LIST_HEAD(&kvm->devices);
> -
>       r = kvm_init_mmu_notifier(kvm);
>       if (r)
>               goto out_err;