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

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Message-ID: <d322c7d4-9643-a0f4-1575-0cf4c3eb2bc8@linux.ibm.com>
Date:   Fri, 3 Feb 2023 09:26:15 -0500
From:   Matthew Rosato <mjrosato@...ux.ibm.com>
To:     "Liu, Yi L" <yi.l.liu@...el.com>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "jgg@...dia.com" <jgg@...dia.com>
Cc:     "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>,
        "Tian, Kevin" <kevin.tian@...el.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 2/3/23 3:58 AM, Liu, Yi L wrote:
> Hi Matthew,
> 
...
>> * Can't pass group->kvm to vfio_device_open, as it references the value
>>   outside of new lock.  Pass device->kvm to minimize changes in this
>>   fix (Alex, Yi)
...
>> @@ -361,7 +420,6 @@ static int vfio_device_first_open(struct vfio_device
>> *device,
>>  	if (ret)
>>  		goto err_module_put;
>>
>> -	device->kvm = kvm;
> 
> Since you've deleted the only usage of kvm pointer in this function, I
> guess you can remove the kvm parameter from vfio_device_open()
> and vfio_device_first_open(). :-) if it makes this patch too big, may
> just have another patch to do it.
> 

Hi Yi,

Yeah, I mentioned it briefly (and vaguely I guess) in the cover, that was intentionally left out to reduce the patch size since this is a fix.  I thought that was the consensus from the v2 comments anyway.

If I end up doing a v4 for this I can just include the removal as a 2nd patch (without a fixes tag) and Alex can squash or keep separate as preferred -- if not you can feel free to do that removal with your cdev follow-up that exploits this work.   

Thanks,
Matt