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Date: Tue, 25 Jul 2017 14:07:25 -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 v1 11/13] xen/pvcalls: implement release command
On Mon, 24 Jul 2017, Juergen Gross wrote:
> On 22/07/17 02:12, Stefano Stabellini wrote:
> > Send PVCALLS_RELEASE to the backend and wait for a reply. Take both
> > in_mutex and out_mutex to avoid concurrent accesses. Then, free the
> > socket.
> >
> > Signed-off-by: Stefano Stabellini <stefano@...reto.com>
> > CC: boris.ostrovsky@...cle.com
> > CC: jgross@...e.com
> > ---
> > drivers/xen/pvcalls-front.c | 86 +++++++++++++++++++++++++++++++++++++++++++++
> > drivers/xen/pvcalls-front.h | 1 +
> > 2 files changed, 87 insertions(+)
> >
> > diff --git a/drivers/xen/pvcalls-front.c b/drivers/xen/pvcalls-front.c
> > index b6cfb7d..bd3dfac 100644
> > --- a/drivers/xen/pvcalls-front.c
> > +++ b/drivers/xen/pvcalls-front.c
> > @@ -174,6 +174,24 @@ static irqreturn_t pvcalls_front_conn_handler(int irq, void *sock_map)
> > return IRQ_HANDLED;
> > }
> >
> > +static void pvcalls_front_free_map(struct pvcalls_bedata *bedata,
> > + struct sock_mapping *map)
> > +{
> > + int i;
> > +
> > + spin_lock(&bedata->pvcallss_lock);
> > + if (!list_empty(&map->list))
> > + list_del_init(&map->list);
> > + spin_unlock(&bedata->pvcallss_lock);
> > +
> > + /* what if the thread waiting still need access? */
>
> Is this handled? If not, why is it no problem?
Yes, sorry. This is a left-over from earlier versions of the code.
This scenario is handled because threads waiting will have already been
awaken by the wake_up_interruptible call in pvcalls_front_release, and
also the code is protected by both the in_mutex and out_mutex. I hadn't
introduced in_mutex and out_mutex yet when I wrote this comment, it no
longer applies.
> > + for (i = 0; i < (1 << map->active.ring->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);
> > + unbind_from_irqhandler(map->active.irq, map);
> > +}
> > +
> > int pvcalls_front_socket(struct socket *sock)
> > {
> > struct pvcalls_bedata *bedata;
> > @@ -805,6 +823,74 @@ unsigned int pvcalls_front_poll(struct file *file, struct socket *sock,
> > return pvcalls_front_poll_passive(file, bedata, map, wait);
> > }
> >
> > +int pvcalls_front_release(struct socket *sock)
> > +{
> > + struct pvcalls_bedata *bedata;
> > + struct sock_mapping *map;
> > + int req_id, notify;
> > + struct xen_pvcalls_request *req;
> > +
> > + if (!pvcalls_front_dev)
> > + return -EIO;
> > + bedata = dev_get_drvdata(&pvcalls_front_dev->dev);
> > + if (!bedata)
> > + return -EIO;
> > +
> > + if (sock->sk == NULL)
> > + return 0;
> > +
> > + map = (struct sock_mapping *) READ_ONCE(sock->sk->sk_send_head);
> > + if (map == NULL)
> > + return 0;
> > + WRITE_ONCE(sock->sk->sk_send_head, NULL);
> > +
> > + spin_lock(&bedata->pvcallss_lock);
> > + req_id = bedata->ring.req_prod_pvt & (RING_SIZE(&bedata->ring) - 1);
> > + BUG_ON(req_id >= PVCALLS_NR_REQ_PER_RING);
> > + if (RING_FULL(&bedata->ring) ||
> > + READ_ONCE(bedata->rsp[req_id].req_id) != PVCALLS_INVALID_ID) {
> > + spin_unlock(&bedata->pvcallss_lock);
> > + return -EAGAIN;
>
> Isn't it a problem you already cleared sock->sk->sk_send_head?
Yes, you are right. It would effectively leak the socket. I'll move the
clearing of sk_send_head after this check.
> > + }
> > + req = RING_GET_REQUEST(&bedata->ring, req_id);
> > + req->req_id = req_id;
> > + req->cmd = PVCALLS_RELEASE;
> > + req->u.release.id = (uint64_t)sock;
> > +
> > + bedata->ring.req_prod_pvt++;
> > + RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(&bedata->ring, notify);
> > + spin_unlock(&bedata->pvcallss_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);
> > +
> > + 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);
> > + } else {
> > + spin_lock(&bedata->pvcallss_lock);
> > + list_del_init(&map->list);
> > + kfree(map);
> > + spin_unlock(&bedata->pvcallss_lock);
> > + }
> > + WRITE_ONCE(bedata->rsp[req_id].req_id, PVCALLS_INVALID_ID);
> > +
> > + return 0;
> > +}
> > +
> > static const struct xenbus_device_id pvcalls_front_ids[] = {
> > { "pvcalls" },
> > { "" }
> > diff --git a/drivers/xen/pvcalls-front.h b/drivers/xen/pvcalls-front.h
> > index 25e05b8..3332978 100644
> > --- a/drivers/xen/pvcalls-front.h
> > +++ b/drivers/xen/pvcalls-front.h
> > @@ -23,5 +23,6 @@ int pvcalls_front_recvmsg(struct socket *sock,
> > unsigned int pvcalls_front_poll(struct file *file,
> > struct socket *sock,
> > poll_table *wait);
> > +int pvcalls_front_release(struct socket *sock);
> >
> > #endif
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