Re: [Xen-devel] [PATCH v5 02/13] xen/pvcalls: implement frontend disconnect

[Stefano Stabellini]

On Tue, 17 Oct 2017, Boris Ostrovsky wrote:
> On 10/06/2017 08:30 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.
> >
> > pvcalls_refcount is used to keep count of the outstanding pvcalls users.
> > Only remove connections once the refcount is zero.
> >
> > 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 
> > CC: boris.ostrov...@oracle.com
> > CC: jgr...@suse.com
> > ---
> >  drivers/xen/pvcalls-front.c | 67 
> > +
> >  1 file changed, 67 insertions(+)
> >
> > diff --git a/drivers/xen/pvcalls-front.c b/drivers/xen/pvcalls-front.c
> > index a8d38c2..d8b7a04 100644
> > --- a/drivers/xen/pvcalls-front.c
> > +++ b/drivers/xen/pvcalls-front.c
> > @@ -20,6 +20,46 @@
> >  #include 
> >  #include 
> >  
> > +#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 socket_lock;
> > +
> > +   wait_queue_head_t inflight_req;
> > +   struct xen_pvcalls_response rsp[PVCALLS_NR_REQ_PER_RING];
> 
> Did you mean _REQ_ or _RSP_ in the macro name?

For each request there is one response, so it doesn't make a difference.
But for clarity, I will rename.


> > +};
> > +/* Only one front/back connection supported. */
> > +static struct xenbus_device *pvcalls_front_dev;
> > +static atomic_t pvcalls_refcount;
> > +
> > +/* first increment refcount, then proceed */
> > +#define pvcalls_enter() {   \
> > +   atomic_inc(_refcount);  \
> > +}
> > +
> > +/* first complete other operations, then decrement refcount */
> > +#define pvcalls_exit() {\
> > +   atomic_dec(_refcount);  \
> > +}
> > +
> > +static irqreturn_t pvcalls_front_event_handler(int irq, void *dev_id)
> > +{
> > +   return IRQ_HANDLED;
> > +}
> > +
> > +static void pvcalls_front_free_map(struct pvcalls_bedata *bedata,
> > +  struct sock_mapping *map)
> > +{
> > +}
> > +
> >  static const struct xenbus_device_id pvcalls_front_ids[] = {
> > { "pvcalls" },
> > { "" }
> > @@ -27,6 +67,33 @@
> >  
> >  static int pvcalls_front_remove(struct xenbus_device *dev)
> >  {
> > +   struct pvcalls_bedata *bedata;
> > +   struct sock_mapping *map = NULL, *n;
> > +
> > +   bedata = dev_get_drvdata(_front_dev->dev);
> > +   dev_set_drvdata(>dev, NULL);
> > +   pvcalls_front_dev = NULL;
> > +   if (bedata->irq >= 0)
> > +   unbind_from_irqhandler(bedata->irq, dev);
> > +
> > +   smp_mb();
> > +   while (atomic_read(_refcount) > 0)
> > +   cpu_relax();
> > +   list_for_each_entry_safe(map, n, >socket_mappings, list) {
> > +   pvcalls_front_free_map(bedata, map);
> > +   kfree(map);
> > +   }
> > +   list_for_each_entry_safe(map, n, >socketpass_mappings, list) {
> > +   spin_lock(>socket_lock);
> > +   list_del_init(>list);
> > +   spin_unlock(>socket_lock);
> > +   kfree(map);
> 
> Why do you re-init the entry if you are freeing it?

Fair enough, I'll just list_del.


> And do you really
> need the locks around it? This looks similar to the case we've discussed
> for other patches --- if we are concerned that someone may grab this
> entry then something must be wrong.
> 
> (Sorry, this must have been here in earlier versions but I only now
> noticed it.)

Yes, you are right, it is already protected by the global refcount, I'll
remove.


> > +   }
> > +   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;
> >  }
> >  
> 

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Re: [Xen-devel] [PATCH v5 02/13] xen/pvcalls: implement frontend disconnect

[Boris Ostrovsky]

On 10/06/2017 08:30 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.
>
> pvcalls_refcount is used to keep count of the outstanding pvcalls users.
> Only remove connections once the refcount is zero.
>
> 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 
> CC: boris.ostrov...@oracle.com
> CC: jgr...@suse.com
> ---
>  drivers/xen/pvcalls-front.c | 67 
> +
>  1 file changed, 67 insertions(+)
>
> diff --git a/drivers/xen/pvcalls-front.c b/drivers/xen/pvcalls-front.c
> index a8d38c2..d8b7a04 100644
> --- a/drivers/xen/pvcalls-front.c
> +++ b/drivers/xen/pvcalls-front.c
> @@ -20,6 +20,46 @@
>  #include 
>  #include 
>  
> +#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 socket_lock;
> +
> + wait_queue_head_t inflight_req;
> + struct xen_pvcalls_response rsp[PVCALLS_NR_REQ_PER_RING];

Did you mean _REQ_ or _RSP_ in the macro name?

> +};
> +/* Only one front/back connection supported. */
> +static struct xenbus_device *pvcalls_front_dev;
> +static atomic_t pvcalls_refcount;
> +
> +/* first increment refcount, then proceed */
> +#define pvcalls_enter() {   \
> + atomic_inc(_refcount);  \
> +}
> +
> +/* first complete other operations, then decrement refcount */
> +#define pvcalls_exit() {\
> + atomic_dec(_refcount);  \
> +}
> +
> +static irqreturn_t pvcalls_front_event_handler(int irq, void *dev_id)
> +{
> + return IRQ_HANDLED;
> +}
> +
> +static void pvcalls_front_free_map(struct pvcalls_bedata *bedata,
> +struct sock_mapping *map)
> +{
> +}
> +
>  static const struct xenbus_device_id pvcalls_front_ids[] = {
>   { "pvcalls" },
>   { "" }
> @@ -27,6 +67,33 @@
>  
>  static int pvcalls_front_remove(struct xenbus_device *dev)
>  {
> + struct pvcalls_bedata *bedata;
> + struct sock_mapping *map = NULL, *n;
> +
> + bedata = dev_get_drvdata(_front_dev->dev);
> + dev_set_drvdata(>dev, NULL);
> + pvcalls_front_dev = NULL;
> + if (bedata->irq >= 0)
> + unbind_from_irqhandler(bedata->irq, dev);
> +
> + smp_mb();
> + while (atomic_read(_refcount) > 0)
> + cpu_relax();
> + list_for_each_entry_safe(map, n, >socket_mappings, list) {
> + pvcalls_front_free_map(bedata, map);
> + kfree(map);
> + }
> + list_for_each_entry_safe(map, n, >socketpass_mappings, list) {
> + spin_lock(>socket_lock);
> + list_del_init(>list);
> + spin_unlock(>socket_lock);
> + kfree(map);

Why do you re-init the entry if you are freeing it? And do you really
need the locks around it? This looks similar to the case we've discussed
for other patches --- if we are concerned that someone may grab this
entry then something must be wrong.

(Sorry, this must have been here in earlier versions but I only now
noticed it.)

-boris

> + }
> + 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;
>  }
>  


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