Re: [Xen-devel] [PATCH v4 08/13] xen/pvcalls: implement accept command

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

> +int pvcalls_front_accept(struct socket *sock, struct socket *newsock, int 
> flags)
> +{
> +       struct pvcalls_bedata *bedata;
> +       struct sock_mapping *map;
> +       struct sock_mapping *map2 = NULL;
> +       struct xen_pvcalls_request *req;
> +       int notify, req_id, ret, evtchn, nonblock;
> +
> +       pvcalls_enter;
> +       if (!pvcalls_front_dev) {
> +               pvcalls_exit;
> +               return -ENOTCONN;
> +       }
> +       bedata = dev_get_drvdata(&pvcalls_front_dev->dev);
> +
> +       map = (struct sock_mapping *) sock->sk->sk_send_head;
> +       if (!map) {
> +               pvcalls_exit;
> +               return -ENOTSOCK;
> +       }
> +
> +       if (map->passive.status != PVCALLS_STATUS_LISTEN) {
> +               pvcalls_exit;
> +               return -EINVAL;
> +       }
> +
> +       nonblock = flags & SOCK_NONBLOCK;
> +       /*
> +        * Backend only supports 1 inflight accept request, will return
> +        * errors for the others
> +        */
> +       if (test_and_set_bit(PVCALLS_FLAG_ACCEPT_INFLIGHT,
> +                            (void *)&map->passive.flags)) {
> +               req_id = READ_ONCE(map->passive.inflight_req_id);
> +               if (req_id != PVCALLS_INVALID_ID &&
> +                   READ_ONCE(bedata->rsp[req_id].req_id) == req_id) {
> +                       map2 = map->passive.accept_map;
> +                       goto received;
> +               }
> +               if (nonblock) {
> +                       pvcalls_exit;
> +                       return -EAGAIN;
> +               }
> +               if (wait_event_interruptible(map->passive.inflight_accept_req,
> +                       !test_and_set_bit(PVCALLS_FLAG_ACCEPT_INFLIGHT,
> +                                         (void *)&map->passive.flags))) {
> +                       pvcalls_exit;
> +                       return -EINTR;
> +               }
> +       }
> +
> +       spin_lock(&bedata->socket_lock);
> +       ret = get_request(bedata, &req_id);
> +       if (ret < 0) {
> +               spin_unlock(&bedata->socket_lock);
> +               pvcalls_exit;
> +               return ret;
> +       }
> +       map2 = kzalloc(sizeof(*map2), GFP_KERNEL);
> +       if (map2 == NULL) {
> +               spin_unlock(&bedata->socket_lock);
> +               pvcalls_exit;
> +               return -ENOMEM;
> +       }
> +       ret =  create_active(map2, &evtchn);
> +       if (ret < 0) {
> +               kfree(map2);
> +               spin_unlock(&bedata->socket_lock);
> +               pvcalls_exit;
> +               return -ENOMEM;
> +       }
Do you need to clear PVCALLS_FLAG_ACCEPT_INFLIGHT bit on errors (except 
for EAGAIN/EINTR)?
> +       list_add_tail(&map2->list, &bedata->socket_mappings);
> +
> +       req = RING_GET_REQUEST(&bedata->ring, req_id);
> +       req->req_id = req_id;
> +       req->cmd = PVCALLS_ACCEPT;
> +       req->u.accept.id = (uint64_t) map;
> +       req->u.accept.ref = map2->active.ref;
> +       req->u.accept.id_new = (uint64_t) map2;
> +       req->u.accept.evtchn = evtchn;
> +       map->passive.accept_map = map2;
> +
> +       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);
> +       /* We could check if we have received a response before returning. */
> +       if (nonblock) {
> +               WRITE_ONCE(map->passive.inflight_req_id, req_id);
> +               pvcalls_exit;
> +               return -EAGAIN;
> +       }
> +
> +       if (wait_event_interruptible(bedata->inflight_req,
> +               READ_ONCE(bedata->rsp[req_id].req_id) == req_id)) {
> +               pvcalls_exit;
> +               return -EINTR;
> +       }
> +
> +received:
> +       map2->sock = newsock;
> +       newsock->sk = kzalloc(sizeof(*newsock->sk), GFP_KERNEL);
> +       if (!newsock->sk) {
> +               WRITE_ONCE(bedata->rsp[req_id].req_id, PVCALLS_INVALID_ID);
> +               WRITE_ONCE(map->passive.inflight_req_id, PVCALLS_INVALID_ID);
> +               pvcalls_front_free_map(bedata, map2);
> +               kfree(map2);
> +               pvcalls_exit;
> +               return -ENOMEM;
> +       }
> +       newsock->sk->sk_send_head = (void *)map2;
> +
> +       clear_bit(PVCALLS_FLAG_ACCEPT_INFLIGHT, (void *)&map->passive.flags);
> +       wake_up(&map->passive.inflight_accept_req);
> +
> +       ret = bedata->rsp[req_id].ret;
> +       /* read ret, then set this rsp slot to be reused */
> +       smp_mb();
> +       WRITE_ONCE(bedata->rsp[req_id].req_id, PVCALLS_INVALID_ID);
> +       WRITE_ONCE(map->passive.inflight_req_id, PVCALLS_INVALID_ID);
Should inflight_req_id be cleared at the same time as 
PVCALLS_FLAG_ACCEPT_INFLIGHT? They kind of belong together, don't they?
And I wonder whether you actually need the flag --- can you just key off 
map->passive.inflight_req_id not being PVCALLS_INVALID_ID?
(and again, I am not sure about all READ/WRITE_ONCE() macros here).


-boris

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