[PATCH net-next] net: wwan: core: Return poll error in case of port removal

[Loic Poulain <loic.poulain@linaro.org>]

Ensure that the poll system call returns error flags when port is
removed, allowing user side to properly fail, without trying read
or write. Port removal leads to nullified port operations, add a
is_port_connected() helper to safely check the status.

Fixes: 9a44c1cc6388 ("net: Add a WWAN subsystem")
Signed-off-by: Loic Poulain <loic.poulain@linaro.org>
---
 drivers/net/wwan/wwan_core.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/drivers/net/wwan/wwan_core.c b/drivers/net/wwan/wwan_core.c
index 5be5e1e..c965b21 100644
--- a/drivers/net/wwan/wwan_core.c
+++ b/drivers/net/wwan/wwan_core.c
@@ -369,14 +369,25 @@ static int wwan_port_op_tx(struct wwan_port *port, struct sk_buff *skb)
 	return ret;
 }
 
+static bool is_port_connected(struct wwan_port *port)
+{
+	bool connected;
+
+	mutex_lock(&port->ops_lock);
+	connected = !!port->ops;
+	mutex_unlock(&port->ops_lock);
+
+	return connected;
+}
+
 static bool is_read_blocked(struct wwan_port *port)
 {
-	return skb_queue_empty(&port->rxq) && port->ops;
+	return skb_queue_empty(&port->rxq) && is_port_connected(port);
 }
 
 static bool is_write_blocked(struct wwan_port *port)
 {
-	return test_bit(WWAN_PORT_TX_OFF, &port->flags) && port->ops;
+	return test_bit(WWAN_PORT_TX_OFF, &port->flags) && is_port_connected(port);
 }
 
 static int wwan_wait_rx(struct wwan_port *port, bool nonblock)
@@ -508,6 +519,8 @@ static __poll_t wwan_port_fops_poll(struct file *filp, poll_table *wait)
 		mask |= EPOLLOUT | EPOLLWRNORM;
 	if (!is_read_blocked(port))
 		mask |= EPOLLIN | EPOLLRDNORM;
+	if (!is_port_connected(port))
+		mask |= EPOLLHUP | EPOLLERR;
 
 	return mask;
 }
-- 
2.7.4