Re: [PATCH] s390/vfio-ap: do not use open locks during VFIO_GROUP_NOTIFY_SET_KVM notification

[Jason Gunthorpe]

On Tue, Jun 29, 2021 at 09:21:31AM -0400, Jason J. Herne wrote:

> > +	mutex_lock(&matrix_dev->lock);
> > -	if (matrix_mdev->kvm) {
> > -		matrix_mdev->kvm_busy = true;
> > +	if ((matrix_mdev->kvm) && (matrix_mdev->kvm->arch.crypto.crycbd)) {
> >   		mutex_unlock(&matrix_dev->lock);
> 
> 
> If this function cannot be entered concurrently on separate threads then I
> think we can remove this mutex_unlock of matrix_dev->lock, 

Don't remove locking around data. If the data is written under a mutex
it should be read under a mutex too.

Jason