Re: [Xen-devel] [PATCH v4 12/13] xen/pvcalls: implement release command

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

>  
> +static void pvcalls_front_free_map(struct pvcalls_bedata *bedata,
> +                                struct sock_mapping *map)

I just noticed: pvcalls_front_free_map() is referenced by patches 2 and 8.

> +{
> +     int i;
> +
> +     unbind_from_irqhandler(map->active.irq, map);
> +
> +     spin_lock(&bedata->socket_lock);
> +     if (!list_empty(&map->list))
> +             list_del_init(&map->list);
> +     spin_unlock(&bedata->socket_lock);
> +
> +     for (i = 0; i < (1 << PVCALLS_RING_ORDER); i++)
> +             gnttab_end_foreign_access(map->active.ring->ref[i], 0, 0);
> +     gnttab_end_foreign_access(map->active.ref, 0, 0);
> +     free_page((unsigned long)map->active.ring);
> +}
> +
>  int pvcalls_front_socket(struct socket *sock)
>  {
>       struct pvcalls_bedata *bedata;
> @@ -960,6 +978,92 @@ unsigned int pvcalls_front_poll(struct file *file, 
> struct socket *sock,
>       return ret;
>  }
>  
> +int pvcalls_front_release(struct socket *sock)
> +{
> +     struct pvcalls_bedata *bedata;
> +     struct sock_mapping *map;
> +     int req_id, notify, ret;
> +     struct xen_pvcalls_request *req;
> +
> +     pvcalls_enter;
> +     if (!pvcalls_front_dev) {
> +             pvcalls_exit;
> +             return -EIO;
> +     }
> +     if (sock->sk == NULL) {
> +             pvcalls_exit;
> +             return 0;
> +     }
> +
> +     bedata = dev_get_drvdata(&pvcalls_front_dev->dev);
> +
> +     map = (struct sock_mapping *) sock->sk->sk_send_head;
> +     if (map == NULL) {
> +             pvcalls_exit;
> +             return 0;
> +     }
> +
> +     spin_lock(&bedata->socket_lock);
> +     ret = get_request(bedata, &req_id);
> +     if (ret < 0) {
> +             spin_unlock(&bedata->socket_lock);
> +             pvcalls_exit;
> +             return ret;
> +     }
> +     sock->sk->sk_send_head = NULL;
> +
> +     req = RING_GET_REQUEST(&bedata->ring, req_id);
> +     req->req_id = req_id;
> +     req->cmd = PVCALLS_RELEASE;
> +     req->u.release.id = (uint64_t)map;
> +
> +     bedata->ring.req_prod_pvt++;
> +     RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(&bedata->ring, notify);
> +     spin_unlock(&bedata->socket_lock);
> +     if (notify)
> +             notify_remote_via_irq(bedata->irq);
> +
> +     wait_event(bedata->inflight_req,
> +                READ_ONCE(bedata->rsp[req_id].req_id) == req_id);
> +
> +     if (map->active_socket) {
> +             /*
> +              * Set in_error and wake up inflight_conn_req to force
> +              * recvmsg waiters to exit.
> +              */
> +             map->active.ring->in_error = -EBADF;
> +             wake_up_interruptible(&map->active.inflight_conn_req);
> +
> +             /*
> +              * Wait until there are no more waiters on the mutexes.
> +              * We know that no new waiters can be added because sk_send_head
> +              * is set to NULL -- we only need to wait for the existing
> +              * waiters to return.
> +              */
> +             while (!mutex_trylock(&map->active.in_mutex) ||
> +                        !mutex_trylock(&map->active.out_mutex))
> +                     cpu_relax();


What if you manage to grab the locks before waiters get to run? for
example, in recvmsg:

        while (!(flags & MSG_DONTWAIT) && !pvcalls_front_read_todo(map)) {
                wait_event_interruptible(map->active.inflight_conn_req,
                                         pvcalls_front_read_todo(map));
        }
        ret = __read_ring(map->active.ring, &map->active.data,
                          &msg->msg_iter, len, flags);

map will be freed (by pvcalls_front_free_map() below) before __read_ring
is passed the just-freed ring.


> +
> +             pvcalls_front_free_map(bedata, map);
> +             kfree(map);


-boris



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