Date:   Tue, 31 Jan 2023 16:25:30 -0400
From:   Jason Gunthorpe <jgg@nvidia.com>
To:     Matthew Rosato <mjrosato@linux.ibm.com>
Cc:     alex.williamson@redhat.com, pbonzini@redhat.com,
        yi.l.liu@intel.com, cohuck@redhat.com, farman@linux.ibm.com,
        pmorel@linux.ibm.com, borntraeger@linux.ibm.com,
        frankja@linux.ibm.com, imbrenda@linux.ibm.com, david@redhat.com,
        akrowiak@linux.ibm.com, jjherne@linux.ibm.com, pasic@linux.ibm.com,
        zhenyuw@linux.intel.com, zhi.a.wang@intel.com, seanjc@google.com,
        kevin.tian@intel.com, linux-s390@vger.kernel.org,
        kvm@vger.kernel.org, intel-gvt-dev@lists.freedesktop.org,
        intel-gfx@lists.freedesktop.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] vfio: fix deadlock between group lock and kvm lock
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References: <20230131200635.44227-1-mjrosato@linux.ibm.com>
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On Tue, Jan 31, 2023 at 03:06:35PM -0500, Matthew Rosato wrote:
> @@ -799,13 +794,14 @@ EXPORT_SYMBOL_GPL(vfio_file_enforced_coherent);
>  void vfio_file_set_kvm(struct file *file, struct kvm *kvm)
>  {
>  	struct vfio_group *group = file->private_data;
> +	unsigned long flags;
>  
>  	if (!vfio_file_is_group(file))
>  		return;
>  
> -	mutex_lock(&group->group_lock);
> +	spin_lock_irqsave(&group->kvm_ref_lock, flags);
>  	group->kvm = kvm;
> -	mutex_unlock(&group->group_lock);
> +	spin_unlock_irqrestore(&group->kvm_ref_lock, flags);

We know we are in a sleeping context here so these are just
'spin_lock()', same with the other one

Otherwise it seems Ok to me

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>

Jason