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

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Message-ID: <Y9l5OmCRGYZM2nPy@nvidia.com>
Date:   Tue, 31 Jan 2023 16:25:30 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Matthew Rosato <mjrosato@...ux.ibm.com>
Cc:     alex.williamson@...hat.com, pbonzini@...hat.com,
        yi.l.liu@...el.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,
        kevin.tian@...el.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] vfio: fix deadlock between group lock and kvm lock

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@...dia.com>

Jason