linux-kernel - Re: [PATCH] kvm: lock slots_lock around device assignment

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Message-ID: <20120419023008.GB17648@amt.cnet>
Date:	Wed, 18 Apr 2012 23:30:08 -0300
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Alex Williamson <alex.williamson@...hat.com>
Cc:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	jbaron@...hat.com, jan.kiszka@...mens.com
Subject: Re: [PATCH] kvm: lock slots_lock around device assignment

On Tue, Apr 17, 2012 at 09:46:44PM -0600, Alex Williamson wrote:
> @@ -340,7 +343,11 @@ int kvm_iommu_unmap_guest(struct kvm *kvm)
>  	if (!domain)
>  		return 0;
>  
> +	mutex_lock(&kvm->slots_lock);
>  	kvm_iommu_unmap_memslots(kvm);
> +	kvm->arch.iommu_domain = NULL;
> +	mutex_unlock(&kvm->slots_lock);
> +
>  	iommu_domain_free(domain);
>  	return 0;
>  }

This might trigger lockdep warnings due to

kvm_vm_ioctl_create_vcpu
mutex_lock(&kvm->lock)
kvm_put_kvm(kvm)
kvm_destroy_vm
kvm_iommu_unmap_guest 

sequence.

Better drop it, it is not necessary in vm destruction
path (since only user is self).

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