linux-kernel - Re: [PATCH] s390/vfio-ap: do not use open locks during VFIO_GROUP_NOTIFY_SET

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Message-ID: <20210630115508.GB10820@nvidia.com>
Date:   Wed, 30 Jun 2021 08:55:08 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     "Jason J. Herne" <jjherne@...ux.ibm.com>
Cc:     Tony Krowiak <akrowiak@...ux.ibm.com>, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org, borntraeger@...ibm.com,
        cohuck@...hat.com, pasic@...ux.vnet.ibm.com,
        alex.williamson@...hat.com, kwankhede@...dia.com,
        frankja@...ux.ibm.com, david@...hat.com, imbrenda@...ux.ibm.com,
        hca@...ux.ibm.com
Subject: Re: [PATCH] s390/vfio-ap: do not use open locks during
 VFIO_GROUP_NOTIFY_SET_KVM notification

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