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Date: Tue, 13 Jun 2017 17:47:11 -0700 (PDT)
From: Stefano Stabellini <sstabellini@...nel.org>
To: Juergen Gross <jgross@...e.com>
cc: Stefano Stabellini <sstabellini@...nel.org>,
xen-devel@...ts.xen.org, linux-kernel@...r.kernel.org,
boris.ostrovsky@...cle.com,
Stefano Stabellini <stefano@...reto.com>
Subject: Re: [PATCH v3 11/18] xen/pvcalls: implement accept command
On Tue, 13 Jun 2017, Juergen Gross wrote:
> On 02/06/17 21:31, Stefano Stabellini wrote:
> > Implement the accept command by calling inet_accept. To avoid blocking
> > in the kernel, call inet_accept(O_NONBLOCK) from a workqueue, which get
> > scheduled on sk_data_ready (for a passive socket, it means that there
> > are connections to accept).
> >
> > Use the reqcopy field to store the request. Accept the new socket from
> > the delayed work function, create a new sock_mapping for it, map
> > the indexes page and data ring, and reply to the other end. Allocate an
> > ioworker for the socket.
> >
> > Only support one outstanding blocking accept request for every socket at
> > any time.
> >
> > Add a field to sock_mapping to remember the passive socket from which an
> > active socket was created.
> >
> > Signed-off-by: Stefano Stabellini <stefano@...reto.com>
> > CC: boris.ostrovsky@...cle.com
> > CC: jgross@...e.com
> > ---
> > drivers/xen/pvcalls-back.c | 109 ++++++++++++++++++++++++++++++++++++++++++++-
> > 1 file changed, 108 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/xen/pvcalls-back.c b/drivers/xen/pvcalls-back.c
> > index a75586e..f1173f4 100644
> > --- a/drivers/xen/pvcalls-back.c
> > +++ b/drivers/xen/pvcalls-back.c
> > @@ -65,6 +65,7 @@ struct pvcalls_ioworker {
> > struct sock_mapping {
> > struct list_head list;
> > struct pvcalls_fedata *priv;
> > + struct sockpass_mapping *sockpass;
> > struct socket *sock;
> > uint64_t id;
> > grant_ref_t ref;
> > @@ -275,10 +276,79 @@ static int pvcalls_back_release(struct xenbus_device *dev,
> >
> > static void __pvcalls_back_accept(struct work_struct *work)
> > {
> > + struct sockpass_mapping *mappass = container_of(
> > + work, struct sockpass_mapping, register_work);
> > + struct sock_mapping *map;
> > + struct pvcalls_ioworker *iow;
> > + struct pvcalls_fedata *priv;
> > + struct socket *sock;
> > + struct xen_pvcalls_response *rsp;
> > + struct xen_pvcalls_request *req;
> > + int notify;
> > + int ret = -EINVAL;
> > + unsigned long flags;
> > +
> > + priv = mappass->priv;
> > + /* We only need to check the value of "cmd" atomically on read. */
> > + spin_lock_irqsave(&mappass->copy_lock, flags);
> > + req = &mappass->reqcopy;
> > + if (req->cmd != PVCALLS_ACCEPT) {
> > + spin_unlock_irqrestore(&mappass->copy_lock, flags);
> > + return;
> > + }
> > + spin_unlock_irqrestore(&mappass->copy_lock, flags);
>
> What about:
> req = &mappass->reqcopy;
> if (ACCESS_ONCE(req->cmd) != PVCALLS_ACCEPT)
> return;
>
> I can't see the need for taking a lock here.
Sure, good idea
> > +
> > + sock = sock_alloc();
> > + if (sock == NULL)
> > + goto out_error;
> > + sock->type = mappass->sock->type;
> > + sock->ops = mappass->sock->ops;
> > +
> > + ret = inet_accept(mappass->sock, sock, O_NONBLOCK, true);
> > + if (ret == -EAGAIN) {
> > + sock_release(sock);
> > + goto out_error;
> > + }
> > +
> > + map = pvcalls_new_active_socket(priv,
> > + req->u.accept.id_new,
> > + req->u.accept.ref,
> > + req->u.accept.evtchn,
> > + sock);
> > + if (!map) {
> > + sock_release(sock);
> > + goto out_error;
> > + }
> > +
> > + map->sockpass = mappass;
> > + iow = &map->ioworker;
> > + atomic_inc(&map->read);
> > + atomic_inc(&map->io);
> > + queue_work_on(iow->cpu, iow->wq, &iow->register_work);
> > +
> > +out_error:
> > + rsp = RING_GET_RESPONSE(&priv->ring, priv->ring.rsp_prod_pvt++);
> > + rsp->req_id = req->req_id;
> > + rsp->cmd = req->cmd;
> > + rsp->u.accept.id = req->u.accept.id;
> > + rsp->ret = ret;
> > + RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(&priv->ring, notify);
> > + if (notify)
> > + notify_remote_via_irq(priv->irq);
> > +
> > + spin_lock_irqsave(&mappass->copy_lock, flags);
> > + mappass->reqcopy.cmd = 0;
> > + spin_unlock_irqrestore(&mappass->copy_lock, flags);
>
> ACCESS_ONCE(mappass->reqcopy.cmd) = 0;
OK
> > }
> >
> > static void pvcalls_pass_sk_data_ready(struct sock *sock)
> > {
> > + struct sockpass_mapping *mappass = sock->sk_user_data;
> > +
> > + if (mappass == NULL)
> > + return;
> > +
> > + queue_work(mappass->wq, &mappass->register_work);
> > }
> >
> > static int pvcalls_back_bind(struct xenbus_device *dev,
> > @@ -380,7 +450,44 @@ static int pvcalls_back_listen(struct xenbus_device *dev,
> > static int pvcalls_back_accept(struct xenbus_device *dev,
> > struct xen_pvcalls_request *req)
> > {
> > - return 0;
> > + struct pvcalls_fedata *priv;
> > + struct sockpass_mapping *mappass;
> > + int ret = -EINVAL;
> > + struct xen_pvcalls_response *rsp;
> > + unsigned long flags;
> > +
> > + priv = dev_get_drvdata(&dev->dev);
> > +
> > + mappass = radix_tree_lookup(&priv->socketpass_mappings,
> > + req->u.accept.id);
> > + if (mappass == NULL)
> > + goto out_error;
> > +
> > + /*
> > + * Limitation of the current implementation: only support one
> > + * concurrent accept or poll call on one socket.
> > + */
> > + spin_lock_irqsave(&mappass->copy_lock, flags);
> > + if (mappass->reqcopy.cmd != 0) {
> > + spin_unlock_irqrestore(&mappass->copy_lock, flags);
> > + ret = -EINTR;
> > + goto out_error;
> > + }
> > +
> > + mappass->reqcopy = *req;
>
> This time you need the lock, however you should use:
>
> ACCESS_ONCE(mappass->reqcopy) = *req;
I don't think that guarantees atomic accesses to the cmd field of the
struct. Shouldn't this be:
ACCESS_ONCE(mappass->reqcopy.cmd) = req->cmd;
mappass->reqcopy = *req;
> > + spin_unlock_irqrestore(&mappass->copy_lock, flags);
> > + queue_work(mappass->wq, &mappass->register_work);
> > +
> > + /* Tell the caller we don't need to send back a notification yet */
> > + return -1;
> > +
> > +out_error:
> > + rsp = RING_GET_RESPONSE(&priv->ring, priv->ring.rsp_prod_pvt++);
> > + rsp->req_id = req->req_id;
> > + rsp->cmd = req->cmd;
> > + rsp->u.accept.id = req->u.accept.id;
> > + rsp->ret = ret;
> > + return ret;
>
> return 0?
Yes, thanks
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