netfront: plug a theoretical leak on setup_device()'s error path

Suppose the frontend is in XenbusStateInitialising and the backend
advances to XenbusStateInitWait. backend_changed() will call
network_connect() -> talk_to_backend() -> setup_device().

If bind_listening_port_to_irqhandler() fails (due to event channel
allocation failure, dynamic IRQ allocation failure etc), then the
grant references and the shared ring pages remain allocated. The error
percolates back to backend_changed() without any cleanup.
backend_changed() will not change the frontend state; it will stay in
XenbusStateInitialising. If the backend retries XenbusStateInitWait
(possibly through a fake, no-op mediate state, like
XenbusStateClosed), then the frontend repeats the above call chain and
leaks the previously unreleased ring pages and grant references.

If setup_device() fails to grant access to the RX page before it tries
to call bind_listening_port_to_irqhandler(), then only the TX page /
grant reference are leaked in the next round.

I'm not sure what happens when the RX page allocation fails:
xenbus_dev_fatal() is called then, which changes the frontend's state
and seems to preclude a second immediate call to network_connect(). I
think this patch shouldn't hurt in that case either (or after
earlier failures in setup_device() for that matter).

Signed-off-by: Laszlo Ersek <lersek@redhat.com>

diff --git a/drivers/xen/netfront/netfront.c b/drivers/xen/netfront/netfront.c
index 46b79961f3e3a35cd3af01fd66c5c7c0c48edf41..f1605355c0882ced8710c3bf1849f7fe1f73625e 100644 (file)
--- a/drivers/xen/netfront/netfront.c
+++ b/drivers/xen/netfront/netfront.c
@@ -215,6 +215,7 @@ static int setup_device(struct xenbus_device *, struct netfront_info *);
 static struct net_device *create_netdev(struct xenbus_device *);
 
 static void end_access(int, void *);
+static void netif_release_rings(struct netfront_info *);
 static void netif_disconnect_backend(struct netfront_info *);
 
 static int network_connect(struct net_device *);
@@ -522,6 +523,7 @@ static int setup_device(struct xenbus_device *dev, struct netfront_info *info)
        return 0;
 
  fail:
+       netif_release_rings(info);
        return err;
 }
 
@@ -2152,6 +2154,15 @@ static struct notifier_block notifier_inetdev = {
 };
 #endif
 
+static void netif_release_rings(struct netfront_info *info)
+{
+       end_access(info->tx_ring_ref, info->tx.sring);
+       end_access(info->rx_ring_ref, info->rx.sring);
+       info->tx_ring_ref = GRANT_INVALID_REF;
+       info->rx_ring_ref = GRANT_INVALID_REF;
+       info->tx.sring = NULL;
+       info->rx.sring = NULL;
+}
 
 static void netif_disconnect_backend(struct netfront_info *info)
 {
@@ -2166,12 +2177,7 @@ static void netif_disconnect_backend(struct netfront_info *info)
                unbind_from_irqhandler(info->irq, info->netdev);
        info->irq = 0;
 
-       end_access(info->tx_ring_ref, info->tx.sring);
-       end_access(info->rx_ring_ref, info->rx.sring);
-       info->tx_ring_ref = GRANT_INVALID_REF;
-       info->rx_ring_ref = GRANT_INVALID_REF;
-       info->tx.sring = NULL;
-       info->rx.sring = NULL;
+       netif_release_rings(info);
 }