linux-kernel - Re: [PATCH v4 02/13] xen/pvcalls: implement frontend disconnect

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Date:   Fri, 6 Oct 2017 17:08:41 -0700 (PDT)
From:   Stefano Stabellini <sstabellini@...nel.org>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>
cc:     Stefano Stabellini <sstabellini@...nel.org>,
        xen-devel@...ts.xen.org, linux-kernel@...r.kernel.org,
        jgross@...e.com, Stefano Stabellini <stefano@...reto.com>
Subject: Re: [PATCH v4 02/13] xen/pvcalls: implement frontend disconnect

On Wed, 20 Sep 2017, Boris Ostrovsky wrote:
> >  static int pvcalls_front_remove(struct xenbus_device *dev)
> >  {
> > +	struct pvcalls_bedata *bedata;
> > +	struct sock_mapping *map = NULL, *n;
> > +
> > +	bedata = dev_get_drvdata(&pvcalls_front_dev->dev);
> > +	dev_set_drvdata(&dev->dev, NULL);
> > +	pvcalls_front_dev = NULL;
> 
> One more comment on this patch: should this be the last thing to do?
> pvcalls_front_dev is what prevents pvcalls_front_probe() from proceeding
> and even though I am not sure a probe can be initiated while we are here
> perhaps moving this to the end would make things slightly safer.

pvcalls_front_dev = NULL is set early to prevent most other functions
(connect, listen, etc) from proceeding.

On the other end, pvcalls_front_probe can continue safely in parallel
with pvcalls_front_remove to add a new frontend-backend connection
(which is not supported today anyway). pvcalls_front_probe would be
called with a different xenbus_device parameter.


> > +	if (bedata->irq >= 0)
> > +		unbind_from_irqhandler(bedata->irq, dev);
> > +
> > +	smp_mb();
> > +	while (atomic_read(&pvcalls_refcount) > 0)
> > +		cpu_relax();
> > +	list_for_each_entry_safe(map, n, &bedata->socket_mappings, list) {
> > +		pvcalls_front_free_map(bedata, map);
> > +		kfree(map);
> > +	}
> > +	list_for_each_entry_safe(map, n, &bedata->socketpass_mappings, list) {
> > +		spin_lock(&bedata->socket_lock);
> > +		list_del_init(&map->list);
> > +		spin_unlock(&bedata->socket_lock);
> > +		kfree(map);
> > +	}
> > +	if (bedata->ref >= 0)
> > +		gnttab_end_foreign_access(bedata->ref, 0, 0);
> > +	kfree(bedata->ring.sring);
> > +	kfree(bedata);
> > +	xenbus_switch_state(dev, XenbusStateClosed);
> >  	return 0;
> >  }
> >  
>