linux-kernel - Re: [PATCH v1 11/13] xen/pvcalls: implement release command

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Date:   Mon, 24 Jul 2017 22:14:35 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Stefano Stabellini <sstabellini@...nel.org>,
        xen-devel@...ts.xen.org
Cc:     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 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?

> +	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?


Juergen

> +	}
> +	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
>