linux-kernel - Re: [PATCH v3 02/13] xen/pvcalls: implement frontend disconnect

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Date:   Fri, 8 Sep 2017 17:07:24 -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 v3 02/13] xen/pvcalls: implement frontend disconnect

On Fri, 11 Aug 2017, Boris Ostrovsky wrote:
> On 07/31/2017 06:57 PM, Stefano Stabellini wrote:
> > Introduce a data structure named pvcalls_bedata. It contains pointers to
> > the command ring, the event channel, a list of active sockets and a list
> > of passive sockets. Lists accesses are protected by a spin_lock.
> >
> > Introduce a waitqueue to allow waiting for a response on commands sent
> > to the backend.
> >
> > Introduce an array of struct xen_pvcalls_response to store commands
> > responses.
> >
> > Implement pvcalls frontend removal function. Go through the list of
> > active and passive sockets and free them all, one at a time.
> >
> > Signed-off-by: Stefano Stabellini <stefano@...reto.com>
> > CC: boris.ostrovsky@...cle.com
> > CC: jgross@...e.com
> > ---
> >  drivers/xen/pvcalls-front.c | 51 +++++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 51 insertions(+)
> >
> > diff --git a/drivers/xen/pvcalls-front.c b/drivers/xen/pvcalls-front.c
> > index a8d38c2..a126195 100644
> > --- a/drivers/xen/pvcalls-front.c
> > +++ b/drivers/xen/pvcalls-front.c
> > @@ -20,6 +20,29 @@
> >  #include <xen/xenbus.h>
> >  #include <xen/interface/io/pvcalls.h>
> >  
> > +#define PVCALLS_INVALID_ID UINT_MAX
> > +#define PVCALLS_RING_ORDER XENBUS_MAX_RING_GRANT_ORDER
> > +#define PVCALLS_NR_REQ_PER_RING __CONST_RING_SIZE(xen_pvcalls, XEN_PAGE_SIZE)
> > +
> > +struct pvcalls_bedata {
> > +	struct xen_pvcalls_front_ring ring;
> > +	grant_ref_t ref;
> > +	int irq;
> > +
> > +	struct list_head socket_mappings;
> > +	struct list_head socketpass_mappings;
> > +	spinlock_t pvcallss_lock;
> 
> In the backend this is called socket_lock and (subjectively) it would
> sound as a better name here too.

I'll rename


> > +
> > +	wait_queue_head_t inflight_req;
> > +	struct xen_pvcalls_response rsp[PVCALLS_NR_REQ_PER_RING];
> > +};
> > +static struct xenbus_device *pvcalls_front_dev;
> > +
> > +static irqreturn_t pvcalls_front_event_handler(int irq, void *dev_id)
> > +{
> > +	return IRQ_HANDLED;
> > +}
> > +
> >  static const struct xenbus_device_id pvcalls_front_ids[] = {
> >  	{ "pvcalls" },
> >  	{ "" }
> > @@ -27,6 +50,34 @@
> >  
> >  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);
> > +
> > +	list_for_each_entry_safe(map, n, &bedata->socket_mappings, list) {
> > +		mutex_lock(&map->active.in_mutex);
> > +		mutex_lock(&map->active.out_mutex);
> > +		pvcalls_front_free_map(bedata, map);
> > +		mutex_unlock(&map->active.out_mutex);
> > +		mutex_unlock(&map->active.in_mutex);
> > +		kfree(map);
> 
> I think this is the same issue as the one discussed for some other patch
> --- unlocking and then immediately freeing a lock.

Yes, I'll fix this too.


> > +	}
> > +	list_for_each_entry_safe(map, n, &bedata->socketpass_mappings, list) {
> > +		spin_lock(&bedata->pvcallss_lock);
> > +		list_del_init(&map->list);
> > +		spin_unlock(&bedata->pvcallss_lock);
> > +		kfree(map);
> > +	}
> > +	if (bedata->irq > 0)
> > +		unbind_from_irqhandler(bedata->irq, dev);
> > +	if (bedata->ref >= 0)
> > +		gnttab_end_foreign_access(bedata->ref, 0, 0);
> > +	kfree(bedata->ring.sring);
> > +	kfree(bedata);
> > +	dev_set_drvdata(&dev->dev, NULL);
> > +	xenbus_switch_state(dev, XenbusStateClosed);
> 
> Should we first move the state to Closed and then free things up? Or it
> doesn't matter?

I believe that is already done by the xenbus driver: this function is
supposed to be called after the frontend state is set to Closing.


> > +	pvcalls_front_dev = NULL;
> >  	return 0;
> >  }
> >  
>