linux-kernel - Re: [PATCH v3] vfio: fix deadlock between group lock and kvm lock

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Date:   Fri, 3 Feb 2023 14:35:51 -0700
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Matthew Rosato <mjrosato@...ux.ibm.com>
Cc:     "Liu, Yi L" <yi.l.liu@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "jgg@...dia.com" <jgg@...dia.com>,
        "cohuck@...hat.com" <cohuck@...hat.com>,
        "farman@...ux.ibm.com" <farman@...ux.ibm.com>,
        "pmorel@...ux.ibm.com" <pmorel@...ux.ibm.com>,
        "borntraeger@...ux.ibm.com" <borntraeger@...ux.ibm.com>,
        "frankja@...ux.ibm.com" <frankja@...ux.ibm.com>,
        "imbrenda@...ux.ibm.com" <imbrenda@...ux.ibm.com>,
        "david@...hat.com" <david@...hat.com>,
        "akrowiak@...ux.ibm.com" <akrowiak@...ux.ibm.com>,
        "jjherne@...ux.ibm.com" <jjherne@...ux.ibm.com>,
        "pasic@...ux.ibm.com" <pasic@...ux.ibm.com>,
        "zhenyuw@...ux.intel.com" <zhenyuw@...ux.intel.com>,
        "Wang, Zhi A" <zhi.a.wang@...el.com>,
        "Christopherson, , Sean" <seanjc@...gle.com>,
        "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "intel-gvt-dev@...ts.freedesktop.org" 
        <intel-gvt-dev@...ts.freedesktop.org>,
        "intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] vfio: fix deadlock between group lock and kvm lock

On Fri, 3 Feb 2023 16:19:10 -0500
Matthew Rosato <mjrosato@...ux.ibm.com> wrote:
> > @@ -350,32 +350,25 @@ void vfio_device_get_kvm_safe(struct vfio_device *device)
> >  
> >  	lockdep_assert_held(&device->dev_set->lock);
> >  
> > -	spin_lock(&device->group->kvm_ref_lock);
> > -	if (!device->group->kvm)
> > -		goto unlock;
> > -
> >  	pfn = symbol_get(kvm_put_kvm);
> >  	if (WARN_ON(!pfn))
> > -		goto unlock;
> > +		return;
> >  
> >  	fn = symbol_get(kvm_get_kvm_safe);
> >  	if (WARN_ON(!fn)) {
> >  		symbol_put(kvm_put_kvm);
> > -		goto unlock;
> > +		return;
> >  	}  
> >  >  	ret = fn(device->group->kvm);  
> 
> s/device->group->kvm/kvm/

Oops, yes.

> With that small change, this looks good to me too (and testing looks
> good too).  Do you want me to send a v4 for one last round of review?

Please do.  Thanks,

Alex