[PATCH 0/2] pvcalls-front improvements

[PATCH 0/2] pvcalls-front improvements

[Stefano Stabellini]

Hi all,

this small series introduces a per socket refcount to increase the
efficiency on socket release operations, and makes releasing passive
sockets safe.

Cheers,

Stefano


Stefano Stabellini (2):
      pvcalls-front: introduce a per sock_mapping refcount
      pvcalls-front: wait for other operations to return when release passive sockets

 drivers/xen/pvcalls-front.c | 196 +++++++++++++++++++-------------------------
 1 file changed, 84 insertions(+), 112 deletions(-)

[PATCH 1/2] pvcalls-front: introduce a per sock_mapping refcount

[Stefano Stabellini]

Introduce a per sock_mapping refcount, in addition to the existing
global refcount. Thanks to the sock_mapping refcount, we can safely wait
for it to be 1 in pvcalls_front_release before freeing an active socket,
instead of waiting for the global refcount to be 1.

Signed-off-by: Stefano Stabellini <stefano@aporeto.com>
---
 drivers/xen/pvcalls-front.c | 190 ++++++++++++++++++--------------------------
 1 file changed, 78 insertions(+), 112 deletions(-)

diff --git a/drivers/xen/pvcalls-front.c b/drivers/xen/pvcalls-front.c
index 4c789e6..164d3ad 100644
--- a/drivers/xen/pvcalls-front.c
+++ b/drivers/xen/pvcalls-front.c
@@ -60,6 +60,7 @@ struct sock_mapping {
 	bool active_socket;
 	struct list_head list;
 	struct socket *sock;
+	atomic_t refcount;
 	union {
 		struct {
 			int irq;
@@ -93,6 +94,33 @@ struct sock_mapping {
 	};
 };
 
+static inline struct sock_mapping *pvcalls_enter_sock(struct socket *sock)
+{
+	struct sock_mapping *map = NULL;
+
+	if (!pvcalls_front_dev || &pvcalls_front_dev->dev == NULL)
+		return ERR_PTR(-ENOTCONN);
+
+	pvcalls_enter();
+	map = (struct sock_mapping *) sock->sk->sk_send_head;
+	if (map == NULL) {
+		pvcalls_exit()
+		return ERR_PTR(-ENOTSOCK);
+	}
+
+	atomic_inc(&map->refcount);
+	return map;
+}
+
+static inline void pvcalls_exit_sock(struct socket *sock)
+{
+	struct sock_mapping *map = NULL;
+
+	map = (struct sock_mapping *) sock->sk->sk_send_head;
+	atomic_dec(&map->refcount);
+	pvcalls_exit();
+}
+
 static inline int get_request(struct pvcalls_bedata *bedata, int *req_id)
 {
 	*req_id = bedata->ring.req_prod_pvt & (RING_SIZE(&bedata->ring) - 1);
@@ -369,31 +397,23 @@ int pvcalls_front_connect(struct socket *sock, struct sockaddr *addr,
 	if (addr->sa_family != AF_INET || sock->type != SOCK_STREAM)
 		return -EOPNOTSUPP;
 
-	pvcalls_enter();
-	if (!pvcalls_front_dev) {
-		pvcalls_exit();
-		return -ENOTCONN;
-	}
+	map = pvcalls_enter_sock(sock);
+	if (IS_ERR(map))
+		return PTR_ERR(map);
 
 	bedata = dev_get_drvdata(&pvcalls_front_dev->dev);
 
-	map = (struct sock_mapping *)sock->sk->sk_send_head;
-	if (!map) {
-		pvcalls_exit();
-		return -ENOTSOCK;
-	}
-
 	spin_lock(&bedata->socket_lock);
 	ret = get_request(bedata, &req_id);
 	if (ret < 0) {
 		spin_unlock(&bedata->socket_lock);
-		pvcalls_exit();
+		pvcalls_exit_sock(sock);
 		return ret;
 	}
 	ret = create_active(map, &evtchn);
 	if (ret < 0) {
 		spin_unlock(&bedata->socket_lock);
-		pvcalls_exit();
+		pvcalls_exit_sock(sock);
 		return ret;
 	}
 
@@ -423,7 +443,7 @@ int pvcalls_front_connect(struct socket *sock, struct sockaddr *addr,
 	smp_rmb();
 	ret = bedata->rsp[req_id].ret;
 	bedata->rsp[req_id].req_id = PVCALLS_INVALID_ID;
-	pvcalls_exit();
+	pvcalls_exit_sock(sock);
 	return ret;
 }
 
@@ -488,23 +508,15 @@ int pvcalls_front_sendmsg(struct socket *sock, struct msghdr *msg,
 	if (flags & (MSG_CONFIRM|MSG_DONTROUTE|MSG_EOR|MSG_OOB))
 		return -EOPNOTSUPP;
 
-	pvcalls_enter();
-	if (!pvcalls_front_dev) {
-		pvcalls_exit();
-		return -ENOTCONN;
-	}
+	map = pvcalls_enter_sock(sock);
+	if (IS_ERR(map))
+		return PTR_ERR(map);
 	bedata = dev_get_drvdata(&pvcalls_front_dev->dev);
 
-	map = (struct sock_mapping *) sock->sk->sk_send_head;
-	if (!map) {
-		pvcalls_exit();
-		return -ENOTSOCK;
-	}
-
 	mutex_lock(&map->active.out_mutex);
 	if ((flags & MSG_DONTWAIT) && !pvcalls_front_write_todo(map)) {
 		mutex_unlock(&map->active.out_mutex);
-		pvcalls_exit();
+		pvcalls_exit_sock(sock);
 		return -EAGAIN;
 	}
 	if (len > INT_MAX)
@@ -526,7 +538,7 @@ int pvcalls_front_sendmsg(struct socket *sock, struct msghdr *msg,
 		tot_sent = sent;
 
 	mutex_unlock(&map->active.out_mutex);
-	pvcalls_exit();
+	pvcalls_exit_sock(sock);
 	return tot_sent;
 }
 
@@ -591,19 +603,11 @@ int pvcalls_front_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
 	if (flags & (MSG_CMSG_CLOEXEC|MSG_ERRQUEUE|MSG_OOB|MSG_TRUNC))
 		return -EOPNOTSUPP;
 
-	pvcalls_enter();
-	if (!pvcalls_front_dev) {
-		pvcalls_exit();
-		return -ENOTCONN;
-	}
+	map = pvcalls_enter_sock(sock);
+	if (IS_ERR(map))
+		return PTR_ERR(map);
 	bedata = dev_get_drvdata(&pvcalls_front_dev->dev);
 
-	map = (struct sock_mapping *) sock->sk->sk_send_head;
-	if (!map) {
-		pvcalls_exit();
-		return -ENOTSOCK;
-	}
-
 	mutex_lock(&map->active.in_mutex);
 	if (len > XEN_FLEX_RING_SIZE(PVCALLS_RING_ORDER))
 		len = XEN_FLEX_RING_SIZE(PVCALLS_RING_ORDER);
@@ -623,7 +627,7 @@ int pvcalls_front_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
 		ret = 0;
 
 	mutex_unlock(&map->active.in_mutex);
-	pvcalls_exit();
+	pvcalls_exit_sock(sock);
 	return ret;
 }
 
@@ -637,24 +641,16 @@ int pvcalls_front_bind(struct socket *sock, struct sockaddr *addr, int addr_len)
 	if (addr->sa_family != AF_INET || sock->type != SOCK_STREAM)
 		return -EOPNOTSUPP;
 
-	pvcalls_enter();
-	if (!pvcalls_front_dev) {
-		pvcalls_exit();
-		return -ENOTCONN;
-	}
+	map = pvcalls_enter_sock(sock);
+	if (IS_ERR(map))
+		return PTR_ERR(map);
 	bedata = dev_get_drvdata(&pvcalls_front_dev->dev);
 
-	map = (struct sock_mapping *) sock->sk->sk_send_head;
-	if (map == NULL) {
-		pvcalls_exit();
-		return -ENOTSOCK;
-	}
-
 	spin_lock(&bedata->socket_lock);
 	ret = get_request(bedata, &req_id);
 	if (ret < 0) {
 		spin_unlock(&bedata->socket_lock);
-		pvcalls_exit();
+		pvcalls_exit_sock(sock);
 		return ret;
 	}
 	req = RING_GET_REQUEST(&bedata->ring, req_id);
@@ -684,7 +680,7 @@ int pvcalls_front_bind(struct socket *sock, struct sockaddr *addr, int addr_len)
 	bedata->rsp[req_id].req_id = PVCALLS_INVALID_ID;
 
 	map->passive.status = PVCALLS_STATUS_BIND;
-	pvcalls_exit();
+	pvcalls_exit_sock(sock);
 	return 0;
 }
 
@@ -695,21 +691,13 @@ int pvcalls_front_listen(struct socket *sock, int backlog)
 	struct xen_pvcalls_request *req;
 	int notify, req_id, ret;
 
-	pvcalls_enter();
-	if (!pvcalls_front_dev) {
-		pvcalls_exit();
-		return -ENOTCONN;
-	}
+	map = pvcalls_enter_sock(sock);
+	if (IS_ERR(map))
+		return PTR_ERR(map);
 	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_BIND) {
-		pvcalls_exit();
+		pvcalls_exit_sock(sock);
 		return -EOPNOTSUPP;
 	}
 
@@ -717,7 +705,7 @@ int pvcalls_front_listen(struct socket *sock, int backlog)
 	ret = get_request(bedata, &req_id);
 	if (ret < 0) {
 		spin_unlock(&bedata->socket_lock);
-		pvcalls_exit();
+		pvcalls_exit_sock(sock);
 		return ret;
 	}
 	req = RING_GET_REQUEST(&bedata->ring, req_id);
@@ -741,7 +729,7 @@ int pvcalls_front_listen(struct socket *sock, int backlog)
 	bedata->rsp[req_id].req_id = PVCALLS_INVALID_ID;
 
 	map->passive.status = PVCALLS_STATUS_LISTEN;
-	pvcalls_exit();
+	pvcalls_exit_sock(sock);
 	return ret;
 }
 
@@ -753,21 +741,13 @@ int pvcalls_front_accept(struct socket *sock, struct socket *newsock, int flags)
 	struct xen_pvcalls_request *req;
 	int notify, req_id, ret, evtchn, nonblock;
 
-	pvcalls_enter();
-	if (!pvcalls_front_dev) {
-		pvcalls_exit();
-		return -ENOTCONN;
-	}
+	map = pvcalls_enter_sock(sock);
+	if (IS_ERR(map))
+		return PTR_ERR(map);
 	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();
+		pvcalls_exit_sock(sock);
 		return -EINVAL;
 	}
 
@@ -785,13 +765,13 @@ int pvcalls_front_accept(struct socket *sock, struct socket *newsock, int flags)
 			goto received;
 		}
 		if (nonblock) {
-			pvcalls_exit();
+			pvcalls_exit_sock(sock);
 			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();
+			pvcalls_exit_sock(sock);
 			return -EINTR;
 		}
 	}
@@ -802,7 +782,7 @@ int pvcalls_front_accept(struct socket *sock, struct socket *newsock, int flags)
 		clear_bit(PVCALLS_FLAG_ACCEPT_INFLIGHT,
 			  (void *)&map->passive.flags);
 		spin_unlock(&bedata->socket_lock);
-		pvcalls_exit();
+		pvcalls_exit_sock(sock);
 		return ret;
 	}
 	map2 = kzalloc(sizeof(*map2), GFP_ATOMIC);
@@ -810,7 +790,7 @@ int pvcalls_front_accept(struct socket *sock, struct socket *newsock, int flags)
 		clear_bit(PVCALLS_FLAG_ACCEPT_INFLIGHT,
 			  (void *)&map->passive.flags);
 		spin_unlock(&bedata->socket_lock);
-		pvcalls_exit();
+		pvcalls_exit_sock(sock);
 		return -ENOMEM;
 	}
 	ret = create_active(map2, &evtchn);
@@ -819,7 +799,7 @@ int pvcalls_front_accept(struct socket *sock, struct socket *newsock, int flags)
 		clear_bit(PVCALLS_FLAG_ACCEPT_INFLIGHT,
 			  (void *)&map->passive.flags);
 		spin_unlock(&bedata->socket_lock);
-		pvcalls_exit();
+		pvcalls_exit_sock(sock);
 		return ret;
 	}
 	list_add_tail(&map2->list, &bedata->socket_mappings);
@@ -841,13 +821,13 @@ int pvcalls_front_accept(struct socket *sock, struct socket *newsock, int flags)
 	/* We could check if we have received a response before returning. */
 	if (nonblock) {
 		WRITE_ONCE(map->passive.inflight_req_id, req_id);
-		pvcalls_exit();
+		pvcalls_exit_sock(sock);
 		return -EAGAIN;
 	}
 
 	if (wait_event_interruptible(bedata->inflight_req,
 		READ_ONCE(bedata->rsp[req_id].req_id) == req_id)) {
-		pvcalls_exit();
+		pvcalls_exit_sock(sock);
 		return -EINTR;
 	}
 	/* read req_id, then the content */
@@ -862,7 +842,7 @@ int pvcalls_front_accept(struct socket *sock, struct socket *newsock, int flags)
 		clear_bit(PVCALLS_FLAG_ACCEPT_INFLIGHT,
 			  (void *)&map->passive.flags);
 		pvcalls_front_free_map(bedata, map2);
-		pvcalls_exit();
+		pvcalls_exit_sock(sock);
 		return -ENOMEM;
 	}
 	newsock->sk->sk_send_head = (void *)map2;
@@ -874,7 +854,7 @@ int pvcalls_front_accept(struct socket *sock, struct socket *newsock, int flags)
 	clear_bit(PVCALLS_FLAG_ACCEPT_INFLIGHT, (void *)&map->passive.flags);
 	wake_up(&map->passive.inflight_accept_req);
 
-	pvcalls_exit();
+	pvcalls_exit_sock(sock);
 	return ret;
 }
 
@@ -965,23 +945,16 @@ unsigned int pvcalls_front_poll(struct file *file, struct socket *sock,
 	struct sock_mapping *map;
 	int ret;
 
-	pvcalls_enter();
-	if (!pvcalls_front_dev) {
-		pvcalls_exit();
+	map = pvcalls_enter_sock(sock);
+	if (IS_ERR(map))
 		return POLLNVAL;
-	}
 	bedata = dev_get_drvdata(&pvcalls_front_dev->dev);
 
-	map = (struct sock_mapping *) sock->sk->sk_send_head;
-	if (!map) {
-		pvcalls_exit();
-		return POLLNVAL;
-	}
 	if (map->active_socket)
 		ret = pvcalls_front_poll_active(file, bedata, map, wait);
 	else
 		ret = pvcalls_front_poll_passive(file, bedata, map, wait);
-	pvcalls_exit();
+	pvcalls_exit_sock(sock);
 	return ret;
 }
 
@@ -995,25 +968,18 @@ int pvcalls_front_release(struct socket *sock)
 	if (sock->sk == NULL)
 		return 0;
 
-	pvcalls_enter();
-	if (!pvcalls_front_dev) {
-		pvcalls_exit();
+	map = pvcalls_enter_sock(sock);
+	if (IS_ERR(map) && PTR_ERR(map) == -ENOTCONN)
 		return -EIO;
-	}
-
-	bedata = dev_get_drvdata(&pvcalls_front_dev->dev);
-
-	map = (struct sock_mapping *) sock->sk->sk_send_head;
-	if (map == NULL) {
-		pvcalls_exit();
+	if (IS_ERR(map) && PTR_ERR(map) == -ENOTSOCK)
 		return 0;
-	}
+	bedata = dev_get_drvdata(&pvcalls_front_dev->dev);
 
 	spin_lock(&bedata->socket_lock);
 	ret = get_request(bedata, &req_id);
 	if (ret < 0) {
 		spin_unlock(&bedata->socket_lock);
-		pvcalls_exit();
+		pvcalls_exit_sock(sock);
 		return ret;
 	}
 	sock->sk->sk_send_head = NULL;
@@ -1043,10 +1009,10 @@ int pvcalls_front_release(struct socket *sock)
 		/*
 		 * We need to make sure that sendmsg/recvmsg on this socket have
 		 * not started before we've cleared sk_send_head here. The
-		 * easiest (though not optimal) way to guarantee this is to see
-		 * that no pvcall (other than us) is in progress.
+		 * easiest way to guarantee this is to see that no pvcalls
+		 * (other than us) is in progress on this socket.
 		 */
-		while (atomic_read(&pvcalls_refcount) > 1)
+		while (atomic_read(&map->refcount) > 1)
 			cpu_relax();
 
 		pvcalls_front_free_map(bedata, map);
-- 
1.9.1

[PATCH 2/2] pvcalls-front: wait for other operations to return when release passive sockets

[Stefano Stabellini]

Passive sockets can have ongoing operations on them, specifically, we
have two wait_event_interruptable calls in pvcalls_front_accept.

Add two wake_up calls in pvcalls_front_release, then wait for the
potential waiters to return and release the sock_mapping refcount.

Signed-off-by: Stefano Stabellini <stefano@aporeto.com>
---
 drivers/xen/pvcalls-front.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/xen/pvcalls-front.c b/drivers/xen/pvcalls-front.c
index 164d3ad..d32cac5 100644
--- a/drivers/xen/pvcalls-front.c
+++ b/drivers/xen/pvcalls-front.c
@@ -1017,6 +1017,12 @@ int pvcalls_front_release(struct socket *sock)
 
 		pvcalls_front_free_map(bedata, map);
 	} else {
+		wake_up(&bedata->inflight_req);
+		wake_up(&map->passive.inflight_accept_req);
+
+		while (atomic_read(&map->refcount) > 1)
+			cpu_relax();
+
 		spin_lock(&bedata->socket_lock);
 		list_del(&map->list);
 		spin_unlock(&bedata->socket_lock);
-- 
1.9.1

Re: [PATCH 2/2] pvcalls-front: wait for other operations to return when release passive sockets

[Juergen Gross]

On 05/02/18 23:51, Stefano Stabellini wrote:
> Passive sockets can have ongoing operations on them, specifically, we
> have two wait_event_interruptable calls in pvcalls_front_accept.
> 
> Add two wake_up calls in pvcalls_front_release, then wait for the
> potential waiters to return and release the sock_mapping refcount.
> 
> Signed-off-by: Stefano Stabellini <stefano@aporeto.com>

Acked-by: Juergen Gross <jgross@suse.com>


Juergen

Re: [PATCH 2/2] pvcalls-front: wait for other operations to return when release passive sockets

[Stefano Stabellini]

On Mon, 12 Feb 2018, Juergen Gross wrote:
> On 05/02/18 23:51, Stefano Stabellini wrote:
> > Passive sockets can have ongoing operations on them, specifically, we
> > have two wait_event_interruptable calls in pvcalls_front_accept.
> > 
> > Add two wake_up calls in pvcalls_front_release, then wait for the
> > potential waiters to return and release the sock_mapping refcount.
> > 
> > Signed-off-by: Stefano Stabellini <stefano@aporeto.com>
> 
> Acked-by: Juergen Gross <jgross@suse.com>

Thanks!

Re: [PATCH 1/2] pvcalls-front: introduce a per sock_mapping refcount

[Juergen Gross]

On 05/02/18 23:51, Stefano Stabellini wrote:
> Introduce a per sock_mapping refcount, in addition to the existing
> global refcount. Thanks to the sock_mapping refcount, we can safely wait
> for it to be 1 in pvcalls_front_release before freeing an active socket,
> instead of waiting for the global refcount to be 1.
> 
> Signed-off-by: Stefano Stabellini <stefano@aporeto.com>
> ---
>  drivers/xen/pvcalls-front.c | 190 ++++++++++++++++++--------------------------
>  1 file changed, 78 insertions(+), 112 deletions(-)
> 
> diff --git a/drivers/xen/pvcalls-front.c b/drivers/xen/pvcalls-front.c
> index 4c789e6..164d3ad 100644
> --- a/drivers/xen/pvcalls-front.c
> +++ b/drivers/xen/pvcalls-front.c
> @@ -60,6 +60,7 @@ struct sock_mapping {
>  	bool active_socket;
>  	struct list_head list;
>  	struct socket *sock;
> +	atomic_t refcount;
>  	union {
>  		struct {
>  			int irq;
> @@ -93,6 +94,33 @@ struct sock_mapping {
>  	};
>  };
>  
> +static inline struct sock_mapping *pvcalls_enter_sock(struct socket *sock)
> +{
> +	struct sock_mapping *map = NULL;
> +
> +	if (!pvcalls_front_dev || &pvcalls_front_dev->dev == NULL)

Did you mean:
        if (!pvcalls_front_dev || !pvcalls_front_dev->dev)

> +		return ERR_PTR(-ENOTCONN);
> +
> +	pvcalls_enter();
> +	map = (struct sock_mapping *) sock->sk->sk_send_head;

Style: no blank after the cast, please (multiple times).

> +	if (map == NULL) {
> +		pvcalls_exit()
> +		return ERR_PTR(-ENOTSOCK);
> +	}
> +
> +	atomic_inc(&map->refcount);
> +	return map;
> +}
> +
> +static inline void pvcalls_exit_sock(struct socket *sock)
> +{
> +	struct sock_mapping *map = NULL;
> +
> +	map = (struct sock_mapping *) sock->sk->sk_send_head;
> +	atomic_dec(&map->refcount);
> +	pvcalls_exit();
> +}
> +
>  static inline int get_request(struct pvcalls_bedata *bedata, int *req_id)
>  {
>  	*req_id = bedata->ring.req_prod_pvt & (RING_SIZE(&bedata->ring) - 1);
> @@ -369,31 +397,23 @@ int pvcalls_front_connect(struct socket *sock, struct sockaddr *addr,
>  	if (addr->sa_family != AF_INET || sock->type != SOCK_STREAM)
>  		return -EOPNOTSUPP;
>  
> -	pvcalls_enter();
> -	if (!pvcalls_front_dev) {
> -		pvcalls_exit();
> -		return -ENOTCONN;
> -	}
> +	map = pvcalls_enter_sock(sock);
> +	if (IS_ERR(map))
> +		return PTR_ERR(map);
>  
>  	bedata = dev_get_drvdata(&pvcalls_front_dev->dev);
>  
> -	map = (struct sock_mapping *)sock->sk->sk_send_head;
> -	if (!map) {
> -		pvcalls_exit();
> -		return -ENOTSOCK;
> -	}
> -
>  	spin_lock(&bedata->socket_lock);
>  	ret = get_request(bedata, &req_id);
>  	if (ret < 0) {
>  		spin_unlock(&bedata->socket_lock);
> -		pvcalls_exit();
> +		pvcalls_exit_sock(sock);
>  		return ret;
>  	}
>  	ret = create_active(map, &evtchn);
>  	if (ret < 0) {
>  		spin_unlock(&bedata->socket_lock);
> -		pvcalls_exit();
> +		pvcalls_exit_sock(sock);
>  		return ret;
>  	}
>  
> @@ -423,7 +443,7 @@ int pvcalls_front_connect(struct socket *sock, struct sockaddr *addr,
>  	smp_rmb();
>  	ret = bedata->rsp[req_id].ret;
>  	bedata->rsp[req_id].req_id = PVCALLS_INVALID_ID;
> -	pvcalls_exit();
> +	pvcalls_exit_sock(sock);
>  	return ret;
>  }
>  
> @@ -488,23 +508,15 @@ int pvcalls_front_sendmsg(struct socket *sock, struct msghdr *msg,
>  	if (flags & (MSG_CONFIRM|MSG_DONTROUTE|MSG_EOR|MSG_OOB))
>  		return -EOPNOTSUPP;
>  
> -	pvcalls_enter();
> -	if (!pvcalls_front_dev) {
> -		pvcalls_exit();
> -		return -ENOTCONN;
> -	}
> +	map = pvcalls_enter_sock(sock);
> +	if (IS_ERR(map))
> +		return PTR_ERR(map);
>  	bedata = dev_get_drvdata(&pvcalls_front_dev->dev);
>  
> -	map = (struct sock_mapping *) sock->sk->sk_send_head;
> -	if (!map) {
> -		pvcalls_exit();
> -		return -ENOTSOCK;
> -	}
> -
>  	mutex_lock(&map->active.out_mutex);
>  	if ((flags & MSG_DONTWAIT) && !pvcalls_front_write_todo(map)) {
>  		mutex_unlock(&map->active.out_mutex);
> -		pvcalls_exit();
> +		pvcalls_exit_sock(sock);
>  		return -EAGAIN;
>  	}
>  	if (len > INT_MAX)
> @@ -526,7 +538,7 @@ int pvcalls_front_sendmsg(struct socket *sock, struct msghdr *msg,
>  		tot_sent = sent;
>  
>  	mutex_unlock(&map->active.out_mutex);
> -	pvcalls_exit();
> +	pvcalls_exit_sock(sock);
>  	return tot_sent;
>  }
>  
> @@ -591,19 +603,11 @@ int pvcalls_front_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
>  	if (flags & (MSG_CMSG_CLOEXEC|MSG_ERRQUEUE|MSG_OOB|MSG_TRUNC))
>  		return -EOPNOTSUPP;
>  
> -	pvcalls_enter();
> -	if (!pvcalls_front_dev) {
> -		pvcalls_exit();
> -		return -ENOTCONN;
> -	}
> +	map = pvcalls_enter_sock(sock);
> +	if (IS_ERR(map))
> +		return PTR_ERR(map);
>  	bedata = dev_get_drvdata(&pvcalls_front_dev->dev);
>  
> -	map = (struct sock_mapping *) sock->sk->sk_send_head;
> -	if (!map) {
> -		pvcalls_exit();
> -		return -ENOTSOCK;
> -	}
> -
>  	mutex_lock(&map->active.in_mutex);
>  	if (len > XEN_FLEX_RING_SIZE(PVCALLS_RING_ORDER))
>  		len = XEN_FLEX_RING_SIZE(PVCALLS_RING_ORDER);
> @@ -623,7 +627,7 @@ int pvcalls_front_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
>  		ret = 0;
>  
>  	mutex_unlock(&map->active.in_mutex);
> -	pvcalls_exit();
> +	pvcalls_exit_sock(sock);
>  	return ret;
>  }
>  
> @@ -637,24 +641,16 @@ int pvcalls_front_bind(struct socket *sock, struct sockaddr *addr, int addr_len)
>  	if (addr->sa_family != AF_INET || sock->type != SOCK_STREAM)
>  		return -EOPNOTSUPP;
>  
> -	pvcalls_enter();
> -	if (!pvcalls_front_dev) {
> -		pvcalls_exit();
> -		return -ENOTCONN;
> -	}
> +	map = pvcalls_enter_sock(sock);
> +	if (IS_ERR(map))
> +		return PTR_ERR(map);
>  	bedata = dev_get_drvdata(&pvcalls_front_dev->dev);
>  
> -	map = (struct sock_mapping *) sock->sk->sk_send_head;
> -	if (map == NULL) {
> -		pvcalls_exit();
> -		return -ENOTSOCK;
> -	}
> -
>  	spin_lock(&bedata->socket_lock);
>  	ret = get_request(bedata, &req_id);
>  	if (ret < 0) {
>  		spin_unlock(&bedata->socket_lock);
> -		pvcalls_exit();
> +		pvcalls_exit_sock(sock);
>  		return ret;
>  	}
>  	req = RING_GET_REQUEST(&bedata->ring, req_id);
> @@ -684,7 +680,7 @@ int pvcalls_front_bind(struct socket *sock, struct sockaddr *addr, int addr_len)
>  	bedata->rsp[req_id].req_id = PVCALLS_INVALID_ID;
>  
>  	map->passive.status = PVCALLS_STATUS_BIND;
> -	pvcalls_exit();
> +	pvcalls_exit_sock(sock);
>  	return 0;
>  }
>  
> @@ -695,21 +691,13 @@ int pvcalls_front_listen(struct socket *sock, int backlog)
>  	struct xen_pvcalls_request *req;
>  	int notify, req_id, ret;
>  
> -	pvcalls_enter();
> -	if (!pvcalls_front_dev) {
> -		pvcalls_exit();
> -		return -ENOTCONN;
> -	}
> +	map = pvcalls_enter_sock(sock);
> +	if (IS_ERR(map))
> +		return PTR_ERR(map);
>  	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_BIND) {
> -		pvcalls_exit();
> +		pvcalls_exit_sock(sock);
>  		return -EOPNOTSUPP;
>  	}
>  
> @@ -717,7 +705,7 @@ int pvcalls_front_listen(struct socket *sock, int backlog)
>  	ret = get_request(bedata, &req_id);
>  	if (ret < 0) {
>  		spin_unlock(&bedata->socket_lock);
> -		pvcalls_exit();
> +		pvcalls_exit_sock(sock);
>  		return ret;
>  	}
>  	req = RING_GET_REQUEST(&bedata->ring, req_id);
> @@ -741,7 +729,7 @@ int pvcalls_front_listen(struct socket *sock, int backlog)
>  	bedata->rsp[req_id].req_id = PVCALLS_INVALID_ID;
>  
>  	map->passive.status = PVCALLS_STATUS_LISTEN;
> -	pvcalls_exit();
> +	pvcalls_exit_sock(sock);
>  	return ret;
>  }
>  
> @@ -753,21 +741,13 @@ int pvcalls_front_accept(struct socket *sock, struct socket *newsock, int flags)
>  	struct xen_pvcalls_request *req;
>  	int notify, req_id, ret, evtchn, nonblock;
>  
> -	pvcalls_enter();
> -	if (!pvcalls_front_dev) {
> -		pvcalls_exit();
> -		return -ENOTCONN;
> -	}
> +	map = pvcalls_enter_sock(sock);
> +	if (IS_ERR(map))
> +		return PTR_ERR(map);
>  	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();
> +		pvcalls_exit_sock(sock);
>  		return -EINVAL;
>  	}
>  
> @@ -785,13 +765,13 @@ int pvcalls_front_accept(struct socket *sock, struct socket *newsock, int flags)
>  			goto received;
>  		}
>  		if (nonblock) {
> -			pvcalls_exit();
> +			pvcalls_exit_sock(sock);
>  			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();
> +			pvcalls_exit_sock(sock);
>  			return -EINTR;
>  		}
>  	}
> @@ -802,7 +782,7 @@ int pvcalls_front_accept(struct socket *sock, struct socket *newsock, int flags)
>  		clear_bit(PVCALLS_FLAG_ACCEPT_INFLIGHT,
>  			  (void *)&map->passive.flags);
>  		spin_unlock(&bedata->socket_lock);
> -		pvcalls_exit();
> +		pvcalls_exit_sock(sock);
>  		return ret;
>  	}
>  	map2 = kzalloc(sizeof(*map2), GFP_ATOMIC);
> @@ -810,7 +790,7 @@ int pvcalls_front_accept(struct socket *sock, struct socket *newsock, int flags)
>  		clear_bit(PVCALLS_FLAG_ACCEPT_INFLIGHT,
>  			  (void *)&map->passive.flags);
>  		spin_unlock(&bedata->socket_lock);
> -		pvcalls_exit();
> +		pvcalls_exit_sock(sock);
>  		return -ENOMEM;
>  	}
>  	ret = create_active(map2, &evtchn);
> @@ -819,7 +799,7 @@ int pvcalls_front_accept(struct socket *sock, struct socket *newsock, int flags)
>  		clear_bit(PVCALLS_FLAG_ACCEPT_INFLIGHT,
>  			  (void *)&map->passive.flags);
>  		spin_unlock(&bedata->socket_lock);
> -		pvcalls_exit();
> +		pvcalls_exit_sock(sock);
>  		return ret;
>  	}
>  	list_add_tail(&map2->list, &bedata->socket_mappings);
> @@ -841,13 +821,13 @@ int pvcalls_front_accept(struct socket *sock, struct socket *newsock, int flags)
>  	/* We could check if we have received a response before returning. */
>  	if (nonblock) {
>  		WRITE_ONCE(map->passive.inflight_req_id, req_id);
> -		pvcalls_exit();
> +		pvcalls_exit_sock(sock);
>  		return -EAGAIN;
>  	}
>  
>  	if (wait_event_interruptible(bedata->inflight_req,
>  		READ_ONCE(bedata->rsp[req_id].req_id) == req_id)) {
> -		pvcalls_exit();
> +		pvcalls_exit_sock(sock);
>  		return -EINTR;
>  	}
>  	/* read req_id, then the content */
> @@ -862,7 +842,7 @@ int pvcalls_front_accept(struct socket *sock, struct socket *newsock, int flags)
>  		clear_bit(PVCALLS_FLAG_ACCEPT_INFLIGHT,
>  			  (void *)&map->passive.flags);
>  		pvcalls_front_free_map(bedata, map2);
> -		pvcalls_exit();
> +		pvcalls_exit_sock(sock);
>  		return -ENOMEM;
>  	}
>  	newsock->sk->sk_send_head = (void *)map2;
> @@ -874,7 +854,7 @@ int pvcalls_front_accept(struct socket *sock, struct socket *newsock, int flags)
>  	clear_bit(PVCALLS_FLAG_ACCEPT_INFLIGHT, (void *)&map->passive.flags);
>  	wake_up(&map->passive.inflight_accept_req);
>  
> -	pvcalls_exit();
> +	pvcalls_exit_sock(sock);
>  	return ret;
>  }
>  
> @@ -965,23 +945,16 @@ unsigned int pvcalls_front_poll(struct file *file, struct socket *sock,
>  	struct sock_mapping *map;
>  	int ret;
>  
> -	pvcalls_enter();
> -	if (!pvcalls_front_dev) {
> -		pvcalls_exit();
> +	map = pvcalls_enter_sock(sock);
> +	if (IS_ERR(map))
>  		return POLLNVAL;
> -	}
>  	bedata = dev_get_drvdata(&pvcalls_front_dev->dev);
>  
> -	map = (struct sock_mapping *) sock->sk->sk_send_head;
> -	if (!map) {
> -		pvcalls_exit();
> -		return POLLNVAL;
> -	}
>  	if (map->active_socket)
>  		ret = pvcalls_front_poll_active(file, bedata, map, wait);
>  	else
>  		ret = pvcalls_front_poll_passive(file, bedata, map, wait);
> -	pvcalls_exit();
> +	pvcalls_exit_sock(sock);
>  	return ret;
>  }
>  
> @@ -995,25 +968,18 @@ int pvcalls_front_release(struct socket *sock)
>  	if (sock->sk == NULL)
>  		return 0;
>  
> -	pvcalls_enter();
> -	if (!pvcalls_front_dev) {
> -		pvcalls_exit();
> +	map = pvcalls_enter_sock(sock);
> +	if (IS_ERR(map) && PTR_ERR(map) == -ENOTCONN)
>  		return -EIO;
> -	}
> -
> -	bedata = dev_get_drvdata(&pvcalls_front_dev->dev);
> -
> -	map = (struct sock_mapping *) sock->sk->sk_send_head;
> -	if (map == NULL) {
> -		pvcalls_exit();
> +	if (IS_ERR(map) && PTR_ERR(map) == -ENOTSOCK)
>  		return 0;

Hmm, what about:

if (IS_ERR(map)) {
    if (PTR_ERR(map) == -ENOTCONN)
        return -EIO;
    else
        return 0;
}


Juergen

Re: [PATCH 1/2] pvcalls-front: introduce a per sock_mapping refcount

[Stefano Stabellini]

On Mon, 12 Feb 2018, Juergen Gross wrote:
> On 05/02/18 23:51, Stefano Stabellini wrote:
> > Introduce a per sock_mapping refcount, in addition to the existing
> > global refcount. Thanks to the sock_mapping refcount, we can safely wait
> > for it to be 1 in pvcalls_front_release before freeing an active socket,
> > instead of waiting for the global refcount to be 1.
> > 
> > Signed-off-by: Stefano Stabellini <stefano@aporeto.com>
> > ---
> >  drivers/xen/pvcalls-front.c | 190 ++++++++++++++++++--------------------------
> >  1 file changed, 78 insertions(+), 112 deletions(-)
> > 
> > diff --git a/drivers/xen/pvcalls-front.c b/drivers/xen/pvcalls-front.c
> > index 4c789e6..164d3ad 100644
> > --- a/drivers/xen/pvcalls-front.c
> > +++ b/drivers/xen/pvcalls-front.c
> > @@ -60,6 +60,7 @@ struct sock_mapping {
> >  	bool active_socket;
> >  	struct list_head list;
> >  	struct socket *sock;
> > +	atomic_t refcount;
> >  	union {
> >  		struct {
> >  			int irq;
> > @@ -93,6 +94,33 @@ struct sock_mapping {
> >  	};
> >  };
> >  
> > +static inline struct sock_mapping *pvcalls_enter_sock(struct socket *sock)
> > +{
> > +	struct sock_mapping *map = NULL;
> > +
> > +	if (!pvcalls_front_dev || &pvcalls_front_dev->dev == NULL)
> 
> Did you mean:
>         if (!pvcalls_front_dev || !pvcalls_front_dev->dev)

I actually meant:

if (!pvcalls_front_dev || dev_get_drvdata(&pvcalls_front_dev->dev) == NULL)

 
> > +		return ERR_PTR(-ENOTCONN);
> > +
> > +	pvcalls_enter();
> > +	map = (struct sock_mapping *) sock->sk->sk_send_head;
> 
> Style: no blank after the cast, please (multiple times).

OK, I'll fix them all


> > +	if (map == NULL) {
> > +		pvcalls_exit()
> > +		return ERR_PTR(-ENOTSOCK);
> > +	}
> > +
> > +	atomic_inc(&map->refcount);
> > +	return map;
> > +}
> > +
> > +static inline void pvcalls_exit_sock(struct socket *sock)
> > +{
> > +	struct sock_mapping *map = NULL;
> > +
> > +	map = (struct sock_mapping *) sock->sk->sk_send_head;
> > +	atomic_dec(&map->refcount);
> > +	pvcalls_exit();
> > +}
> > +
> >  static inline int get_request(struct pvcalls_bedata *bedata, int *req_id)
> >  {
> >  	*req_id = bedata->ring.req_prod_pvt & (RING_SIZE(&bedata->ring) - 1);
> > @@ -369,31 +397,23 @@ int pvcalls_front_connect(struct socket *sock, struct sockaddr *addr,
> >  	if (addr->sa_family != AF_INET || sock->type != SOCK_STREAM)
> >  		return -EOPNOTSUPP;
> >  
> > -	pvcalls_enter();
> > -	if (!pvcalls_front_dev) {
> > -		pvcalls_exit();
> > -		return -ENOTCONN;
> > -	}
> > +	map = pvcalls_enter_sock(sock);
> > +	if (IS_ERR(map))
> > +		return PTR_ERR(map);
> >  
> >  	bedata = dev_get_drvdata(&pvcalls_front_dev->dev);
> >  
> > -	map = (struct sock_mapping *)sock->sk->sk_send_head;
> > -	if (!map) {
> > -		pvcalls_exit();
> > -		return -ENOTSOCK;
> > -	}
> > -
> >  	spin_lock(&bedata->socket_lock);
> >  	ret = get_request(bedata, &req_id);
> >  	if (ret < 0) {
> >  		spin_unlock(&bedata->socket_lock);
> > -		pvcalls_exit();
> > +		pvcalls_exit_sock(sock);
> >  		return ret;
> >  	}
> >  	ret = create_active(map, &evtchn);
> >  	if (ret < 0) {
> >  		spin_unlock(&bedata->socket_lock);
> > -		pvcalls_exit();
> > +		pvcalls_exit_sock(sock);
> >  		return ret;
> >  	}
> >  
> > @@ -423,7 +443,7 @@ int pvcalls_front_connect(struct socket *sock, struct sockaddr *addr,
> >  	smp_rmb();
> >  	ret = bedata->rsp[req_id].ret;
> >  	bedata->rsp[req_id].req_id = PVCALLS_INVALID_ID;
> > -	pvcalls_exit();
> > +	pvcalls_exit_sock(sock);
> >  	return ret;
> >  }
> >  
> > @@ -488,23 +508,15 @@ int pvcalls_front_sendmsg(struct socket *sock, struct msghdr *msg,
> >  	if (flags & (MSG_CONFIRM|MSG_DONTROUTE|MSG_EOR|MSG_OOB))
> >  		return -EOPNOTSUPP;
> >  
> > -	pvcalls_enter();
> > -	if (!pvcalls_front_dev) {
> > -		pvcalls_exit();
> > -		return -ENOTCONN;
> > -	}
> > +	map = pvcalls_enter_sock(sock);
> > +	if (IS_ERR(map))
> > +		return PTR_ERR(map);
> >  	bedata = dev_get_drvdata(&pvcalls_front_dev->dev);
> >  
> > -	map = (struct sock_mapping *) sock->sk->sk_send_head;
> > -	if (!map) {
> > -		pvcalls_exit();
> > -		return -ENOTSOCK;
> > -	}
> > -
> >  	mutex_lock(&map->active.out_mutex);
> >  	if ((flags & MSG_DONTWAIT) && !pvcalls_front_write_todo(map)) {
> >  		mutex_unlock(&map->active.out_mutex);
> > -		pvcalls_exit();
> > +		pvcalls_exit_sock(sock);
> >  		return -EAGAIN;
> >  	}
> >  	if (len > INT_MAX)
> > @@ -526,7 +538,7 @@ int pvcalls_front_sendmsg(struct socket *sock, struct msghdr *msg,
> >  		tot_sent = sent;
> >  
> >  	mutex_unlock(&map->active.out_mutex);
> > -	pvcalls_exit();
> > +	pvcalls_exit_sock(sock);
> >  	return tot_sent;
> >  }
> >  
> > @@ -591,19 +603,11 @@ int pvcalls_front_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
> >  	if (flags & (MSG_CMSG_CLOEXEC|MSG_ERRQUEUE|MSG_OOB|MSG_TRUNC))
> >  		return -EOPNOTSUPP;
> >  
> > -	pvcalls_enter();
> > -	if (!pvcalls_front_dev) {
> > -		pvcalls_exit();
> > -		return -ENOTCONN;
> > -	}
> > +	map = pvcalls_enter_sock(sock);
> > +	if (IS_ERR(map))
> > +		return PTR_ERR(map);
> >  	bedata = dev_get_drvdata(&pvcalls_front_dev->dev);
> >  
> > -	map = (struct sock_mapping *) sock->sk->sk_send_head;
> > -	if (!map) {
> > -		pvcalls_exit();
> > -		return -ENOTSOCK;
> > -	}
> > -
> >  	mutex_lock(&map->active.in_mutex);
> >  	if (len > XEN_FLEX_RING_SIZE(PVCALLS_RING_ORDER))
> >  		len = XEN_FLEX_RING_SIZE(PVCALLS_RING_ORDER);
> > @@ -623,7 +627,7 @@ int pvcalls_front_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
> >  		ret = 0;
> >  
> >  	mutex_unlock(&map->active.in_mutex);
> > -	pvcalls_exit();
> > +	pvcalls_exit_sock(sock);
> >  	return ret;
> >  }
> >  
> > @@ -637,24 +641,16 @@ int pvcalls_front_bind(struct socket *sock, struct sockaddr *addr, int addr_len)
> >  	if (addr->sa_family != AF_INET || sock->type != SOCK_STREAM)
> >  		return -EOPNOTSUPP;
> >  
> > -	pvcalls_enter();
> > -	if (!pvcalls_front_dev) {
> > -		pvcalls_exit();
> > -		return -ENOTCONN;
> > -	}
> > +	map = pvcalls_enter_sock(sock);
> > +	if (IS_ERR(map))
> > +		return PTR_ERR(map);
> >  	bedata = dev_get_drvdata(&pvcalls_front_dev->dev);
> >  
> > -	map = (struct sock_mapping *) sock->sk->sk_send_head;
> > -	if (map == NULL) {
> > -		pvcalls_exit();
> > -		return -ENOTSOCK;
> > -	}
> > -
> >  	spin_lock(&bedata->socket_lock);
> >  	ret = get_request(bedata, &req_id);
> >  	if (ret < 0) {
> >  		spin_unlock(&bedata->socket_lock);
> > -		pvcalls_exit();
> > +		pvcalls_exit_sock(sock);
> >  		return ret;
> >  	}
> >  	req = RING_GET_REQUEST(&bedata->ring, req_id);
> > @@ -684,7 +680,7 @@ int pvcalls_front_bind(struct socket *sock, struct sockaddr *addr, int addr_len)
> >  	bedata->rsp[req_id].req_id = PVCALLS_INVALID_ID;
> >  
> >  	map->passive.status = PVCALLS_STATUS_BIND;
> > -	pvcalls_exit();
> > +	pvcalls_exit_sock(sock);
> >  	return 0;
> >  }
> >  
> > @@ -695,21 +691,13 @@ int pvcalls_front_listen(struct socket *sock, int backlog)
> >  	struct xen_pvcalls_request *req;
> >  	int notify, req_id, ret;
> >  
> > -	pvcalls_enter();
> > -	if (!pvcalls_front_dev) {
> > -		pvcalls_exit();
> > -		return -ENOTCONN;
> > -	}
> > +	map = pvcalls_enter_sock(sock);
> > +	if (IS_ERR(map))
> > +		return PTR_ERR(map);
> >  	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_BIND) {
> > -		pvcalls_exit();
> > +		pvcalls_exit_sock(sock);
> >  		return -EOPNOTSUPP;
> >  	}
> >  
> > @@ -717,7 +705,7 @@ int pvcalls_front_listen(struct socket *sock, int backlog)
> >  	ret = get_request(bedata, &req_id);
> >  	if (ret < 0) {
> >  		spin_unlock(&bedata->socket_lock);
> > -		pvcalls_exit();
> > +		pvcalls_exit_sock(sock);
> >  		return ret;
> >  	}
> >  	req = RING_GET_REQUEST(&bedata->ring, req_id);
> > @@ -741,7 +729,7 @@ int pvcalls_front_listen(struct socket *sock, int backlog)
> >  	bedata->rsp[req_id].req_id = PVCALLS_INVALID_ID;
> >  
> >  	map->passive.status = PVCALLS_STATUS_LISTEN;
> > -	pvcalls_exit();
> > +	pvcalls_exit_sock(sock);
> >  	return ret;
> >  }
> >  
> > @@ -753,21 +741,13 @@ int pvcalls_front_accept(struct socket *sock, struct socket *newsock, int flags)
> >  	struct xen_pvcalls_request *req;
> >  	int notify, req_id, ret, evtchn, nonblock;
> >  
> > -	pvcalls_enter();
> > -	if (!pvcalls_front_dev) {
> > -		pvcalls_exit();
> > -		return -ENOTCONN;
> > -	}
> > +	map = pvcalls_enter_sock(sock);
> > +	if (IS_ERR(map))
> > +		return PTR_ERR(map);
> >  	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();
> > +		pvcalls_exit_sock(sock);
> >  		return -EINVAL;
> >  	}
> >  
> > @@ -785,13 +765,13 @@ int pvcalls_front_accept(struct socket *sock, struct socket *newsock, int flags)
> >  			goto received;
> >  		}
> >  		if (nonblock) {
> > -			pvcalls_exit();
> > +			pvcalls_exit_sock(sock);
> >  			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();
> > +			pvcalls_exit_sock(sock);
> >  			return -EINTR;
> >  		}
> >  	}
> > @@ -802,7 +782,7 @@ int pvcalls_front_accept(struct socket *sock, struct socket *newsock, int flags)
> >  		clear_bit(PVCALLS_FLAG_ACCEPT_INFLIGHT,
> >  			  (void *)&map->passive.flags);
> >  		spin_unlock(&bedata->socket_lock);
> > -		pvcalls_exit();
> > +		pvcalls_exit_sock(sock);
> >  		return ret;
> >  	}
> >  	map2 = kzalloc(sizeof(*map2), GFP_ATOMIC);
> > @@ -810,7 +790,7 @@ int pvcalls_front_accept(struct socket *sock, struct socket *newsock, int flags)
> >  		clear_bit(PVCALLS_FLAG_ACCEPT_INFLIGHT,
> >  			  (void *)&map->passive.flags);
> >  		spin_unlock(&bedata->socket_lock);
> > -		pvcalls_exit();
> > +		pvcalls_exit_sock(sock);
> >  		return -ENOMEM;
> >  	}
> >  	ret = create_active(map2, &evtchn);
> > @@ -819,7 +799,7 @@ int pvcalls_front_accept(struct socket *sock, struct socket *newsock, int flags)
> >  		clear_bit(PVCALLS_FLAG_ACCEPT_INFLIGHT,
> >  			  (void *)&map->passive.flags);
> >  		spin_unlock(&bedata->socket_lock);
> > -		pvcalls_exit();
> > +		pvcalls_exit_sock(sock);
> >  		return ret;
> >  	}
> >  	list_add_tail(&map2->list, &bedata->socket_mappings);
> > @@ -841,13 +821,13 @@ int pvcalls_front_accept(struct socket *sock, struct socket *newsock, int flags)
> >  	/* We could check if we have received a response before returning. */
> >  	if (nonblock) {
> >  		WRITE_ONCE(map->passive.inflight_req_id, req_id);
> > -		pvcalls_exit();
> > +		pvcalls_exit_sock(sock);
> >  		return -EAGAIN;
> >  	}
> >  
> >  	if (wait_event_interruptible(bedata->inflight_req,
> >  		READ_ONCE(bedata->rsp[req_id].req_id) == req_id)) {
> > -		pvcalls_exit();
> > +		pvcalls_exit_sock(sock);
> >  		return -EINTR;
> >  	}
> >  	/* read req_id, then the content */
> > @@ -862,7 +842,7 @@ int pvcalls_front_accept(struct socket *sock, struct socket *newsock, int flags)
> >  		clear_bit(PVCALLS_FLAG_ACCEPT_INFLIGHT,
> >  			  (void *)&map->passive.flags);
> >  		pvcalls_front_free_map(bedata, map2);
> > -		pvcalls_exit();
> > +		pvcalls_exit_sock(sock);
> >  		return -ENOMEM;
> >  	}
> >  	newsock->sk->sk_send_head = (void *)map2;
> > @@ -874,7 +854,7 @@ int pvcalls_front_accept(struct socket *sock, struct socket *newsock, int flags)
> >  	clear_bit(PVCALLS_FLAG_ACCEPT_INFLIGHT, (void *)&map->passive.flags);
> >  	wake_up(&map->passive.inflight_accept_req);
> >  
> > -	pvcalls_exit();
> > +	pvcalls_exit_sock(sock);
> >  	return ret;
> >  }
> >  
> > @@ -965,23 +945,16 @@ unsigned int pvcalls_front_poll(struct file *file, struct socket *sock,
> >  	struct sock_mapping *map;
> >  	int ret;
> >  
> > -	pvcalls_enter();
> > -	if (!pvcalls_front_dev) {
> > -		pvcalls_exit();
> > +	map = pvcalls_enter_sock(sock);
> > +	if (IS_ERR(map))
> >  		return POLLNVAL;
> > -	}
> >  	bedata = dev_get_drvdata(&pvcalls_front_dev->dev);
> >  
> > -	map = (struct sock_mapping *) sock->sk->sk_send_head;
> > -	if (!map) {
> > -		pvcalls_exit();
> > -		return POLLNVAL;
> > -	}
> >  	if (map->active_socket)
> >  		ret = pvcalls_front_poll_active(file, bedata, map, wait);
> >  	else
> >  		ret = pvcalls_front_poll_passive(file, bedata, map, wait);
> > -	pvcalls_exit();
> > +	pvcalls_exit_sock(sock);
> >  	return ret;
> >  }
> >  
> > @@ -995,25 +968,18 @@ int pvcalls_front_release(struct socket *sock)
> >  	if (sock->sk == NULL)
> >  		return 0;
> >  
> > -	pvcalls_enter();
> > -	if (!pvcalls_front_dev) {
> > -		pvcalls_exit();
> > +	map = pvcalls_enter_sock(sock);
> > +	if (IS_ERR(map) && PTR_ERR(map) == -ENOTCONN)
> >  		return -EIO;
> > -	}
> > -
> > -	bedata = dev_get_drvdata(&pvcalls_front_dev->dev);
> > -
> > -	map = (struct sock_mapping *) sock->sk->sk_send_head;
> > -	if (map == NULL) {
> > -		pvcalls_exit();
> > +	if (IS_ERR(map) && PTR_ERR(map) == -ENOTSOCK)
> >  		return 0;
> 
> Hmm, what about:
> 
> if (IS_ERR(map)) {
>     if (PTR_ERR(map) == -ENOTCONN)
>         return -EIO;
>     else
>         return 0;
> }

Sounds good.