Re: [PATCH] KVM: Fix possible circular locking in kvm_vm_ioctl_assign_device()

[Sheng Yang <sheng@linux.intel.com>]

On Monday 07 December 2009 16:58:04 Sheng Yang wrote:
> One possible order is:
> 
> KVM_CREATE_IRQCHIP ioctl(took kvm->lock) -> kvm_iobus_register_dev() ->
> down_write(kvm->slots_lock).
> 
> The other one is in kvm_vm_ioctl_assign_device(), which take
>  kvm->slots_lock first, then kvm->lock.
> 
> Observe it due to kernel locking debug warnings.
> 
> Signed-off-by: Sheng Yang <sheng@linux.intel.com>

Avi? Marcelo?

-- 
regards
Yang, Sheng

> ---
>  virt/kvm/assigned-dev.c |    6 +++---
>  1 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/virt/kvm/assigned-dev.c b/virt/kvm/assigned-dev.c
> index fd9c097..f73de63 100644
> --- a/virt/kvm/assigned-dev.c
> +++ b/virt/kvm/assigned-dev.c
> @@ -508,8 +508,8 @@ static int kvm_vm_ioctl_assign_device(struct kvm *kvm,
>  	struct kvm_assigned_dev_kernel *match;
>  	struct pci_dev *dev;
> 
> -	down_read(&kvm->slots_lock);
>  	mutex_lock(&kvm->lock);
> +	down_read(&kvm->slots_lock);
> 
>  	match = kvm_find_assigned_dev(&kvm->arch.assigned_dev_head,
>  				      assigned_dev->assigned_dev_id);
> @@ -573,8 +573,8 @@ static int kvm_vm_ioctl_assign_device(struct kvm *kvm,
>  	}
> 
>  out:
> -	mutex_unlock(&kvm->lock);
>  	up_read(&kvm->slots_lock);
> +	mutex_unlock(&kvm->lock);
>  	return r;
>  out_list_del:
>  	list_del(&match->list);
> @@ -585,8 +585,8 @@ out_put:
>  	pci_dev_put(dev);
>  out_free:
>  	kfree(match);
> -	mutex_unlock(&kvm->lock);
>  	up_read(&kvm->slots_lock);
> +	mutex_unlock(&kvm->lock);
>  	return r;
>  }
>