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

From: Eric Dumazet
Date: Mon Mar 21 2016 - 10:47:26 EST


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 <bp@xxxxxxxxx>
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> ---
> 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;