linux-kernel - Re: [PATCH v2] vfio: fix potential deadlock on vfio group lock

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Message-ID: <Y8FvtS3uOFUnSxss@nvidia.com>
Date:   Fri, 13 Jan 2023 10:50:29 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Matthew Rosato <mjrosato@...ux.ibm.com>
Cc:     Alex Williamson <alex.williamson@...hat.com>, pbonzini@...hat.com,
        cohuck@...hat.com, farman@...ux.ibm.com, pmorel@...ux.ibm.com,
        borntraeger@...ux.ibm.com, frankja@...ux.ibm.com,
        imbrenda@...ux.ibm.com, david@...hat.com, akrowiak@...ux.ibm.com,
        jjherne@...ux.ibm.com, pasic@...ux.ibm.com,
        zhenyuw@...ux.intel.com, zhi.a.wang@...el.com, seanjc@...gle.com,
        linux-s390@...r.kernel.org, kvm@...r.kernel.org,
        intel-gvt-dev@...ts.freedesktop.org,
        intel-gfx@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] vfio: fix potential deadlock on vfio group lock

On Thu, Jan 12, 2023 at 04:51:36PM -0500, Matthew Rosato wrote:

> Yep, thanks.  I will surround this bit of code with
> 
> mutex_lock(&device->dev_set->lock);
> ..
> mutex_unlock(&device->dev_set->lock);

Don't do it like that, copy the kvm out of the struct device to the
stack and NULL it. Then do the put without holding any locks.

Jason