RE: [PATCH] vfio: fix deadlock between group lock and kvm lock

[Liu, Yi L]

> From: Jason Gunthorpe <jgg@xxxxxxxxxx>
> Sent: Wednesday, February 1, 2023 4:26 AM
> 
> 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

a dumb question. Why spinlock is required here? 😊

Regards,
Yi Liu