linux-kernel - Re: [PATCH] KVM: fix spin_lock

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Date:	Mon, 21 Mar 2016 07:47:15 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org, bp@...en8.de
Subject: Re: [PATCH] KVM: fix spin_lock_init order on x86

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@...en8.de>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.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;