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 <stef...@aporeto.com>

---
Changes in v2:
- fix code style
- nicer checks in pvcalls_front_release
- fix check in pvcalls_enter_sock
---
 drivers/xen/pvcalls-front.c | 193 +++++++++++++++++++-------------------------
 1 file changed, 81 insertions(+), 112 deletions(-)

diff --git a/drivers/xen/pvcalls-front.c b/drivers/xen/pvcalls-front.c
index 4c789e6..163bf8c 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 +94,34 @@ struct sock_mapping {
        };
 };
 
+static inline struct sock_mapping *pvcalls_enter_sock(struct socket *sock)
+{
+       struct sock_mapping *map = NULL;
+
+       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;
+       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 +398,23 @@ 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 +444,7 @@ 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 +509,15 @@ 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 +539,7 @@ 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 +604,11 @@ 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 +628,7 @@ 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 +642,16 @@ 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 +681,7 @@ 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 +692,13 @@ 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 +706,7 @@ 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 +730,7 @@ 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 +742,13 @@ 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 +766,13 @@ 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 +783,7 @@ 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 +791,7 @@ 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 +800,7 @@ 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 +822,13 @@ 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 +843,7 @@ 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 +855,7 @@ 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 +946,16 @@ 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 +969,20 @@ int pvcalls_front_release(struct socket *sock)
        if (sock->sk == NULL)
                return 0;
 
-       pvcalls_enter();
-       if (!pvcalls_front_dev) {
-               pvcalls_exit();
-               return -EIO;
+       map = pvcalls_enter_sock(sock);
+       if (IS_ERR(map)) {
+               if (PTR_ERR(map) == -ENOTCONN)
+                       return -EIO;
+               else
+                       return 0;
        }
-
        bedata = dev_get_drvdata(&pvcalls_front_dev->dev);
 
-       map = (struct sock_mapping *) sock->sk->sk_send_head;
-       if (map == NULL) {
-               pvcalls_exit();
-               return 0;
-       }
-
        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 +1012,10 @@ 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


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