netdev - [PATCH] net: wwan: fix port open

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Date:   Wed,  4 May 2022 19:50:06 +0530
From:   M Chetan Kumar <m.chetan.kumar@...ux.intel.com>
To:     netdev@...r.kernel.org
Cc:     kuba@...nel.org, davem@...emloft.net, johannes@...solutions.net,
        ryazanov.s.a@...il.com, loic.poulain@...aro.org,
        krishna.c.sudi@...el.com, m.chetan.kumar@...el.com,
        m.chetan.kumar@...ux.intel.com, linuxwwan@...el.com
Subject: [PATCH] net: wwan: fix port open

Wwan device registered port can be opened as many number of times.
The first port open() call binds dev file to driver wwan port device
and subsequent open() call references to same wwan port instance.

When dev file is opened multiple times, all contexts still refers to
same instance of wwan port. So in tx path, the received data will be
fwd to wwan device but in rx path the wwan port has a single rx queue.
Depending on which context goes for early read() the rx data gets
dispatched to it.

Since the wwan port is not handling dispatching of rx data to right
context restrict wwan port open to single context.

Signed-off-by: M Chetan Kumar <m.chetan.kumar@...ux.intel.com>
---
 drivers/net/wwan/wwan_core.c | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/drivers/net/wwan/wwan_core.c b/drivers/net/wwan/wwan_core.c
index b8c7843730ed..9ca2d8d76587 100644
--- a/drivers/net/wwan/wwan_core.c
+++ b/drivers/net/wwan/wwan_core.c
@@ -33,6 +33,7 @@ static struct dentry *wwan_debugfs_dir;
 
 /* WWAN port flags */
 #define WWAN_PORT_TX_OFF	0
+#define WWAN_PORT_OPEN		1
 
 /**
  * struct wwan_device - The structure that defines a WWAN device
@@ -58,7 +59,6 @@ struct wwan_device {
 /**
  * struct wwan_port - The structure that defines a WWAN port
  * @type: Port type
- * @start_count: Port start counter
  * @flags: Store port state and capabilities
  * @ops: Pointer to WWAN port operations
  * @ops_lock: Protect port ops
@@ -70,7 +70,6 @@ struct wwan_device {
  */
 struct wwan_port {
 	enum wwan_port_type type;
-	unsigned int start_count;
 	unsigned long flags;
 	const struct wwan_port_ops *ops;
 	struct mutex ops_lock; /* Serialize ops + protect against removal */
@@ -496,7 +495,7 @@ void wwan_remove_port(struct wwan_port *port)
 	struct wwan_device *wwandev = to_wwan_dev(port->dev.parent);
 
 	mutex_lock(&port->ops_lock);
-	if (port->start_count)
+	if (test_and_clear_bit(WWAN_PORT_OPEN, &port->flags))
 		port->ops->stop(port);
 	port->ops = NULL; /* Prevent any new port operations (e.g. from fops) */
 	mutex_unlock(&port->ops_lock);
@@ -549,11 +548,14 @@ static int wwan_port_op_start(struct wwan_port *port)
 	}
 
 	/* If port is already started, don't start again */
-	if (!port->start_count)
-		ret = port->ops->start(port);
+	if (test_bit(WWAN_PORT_OPEN, &port->flags)) {
+		ret = -EBUSY;
+		goto out_unlock;
+	}
+	ret = port->ops->start(port);
 
 	if (!ret)
-		port->start_count++;
+		set_bit(WWAN_PORT_OPEN, &port->flags);
 
 out_unlock:
 	mutex_unlock(&port->ops_lock);
@@ -564,8 +566,7 @@ static int wwan_port_op_start(struct wwan_port *port)
 static void wwan_port_op_stop(struct wwan_port *port)
 {
 	mutex_lock(&port->ops_lock);
-	port->start_count--;
-	if (!port->start_count) {
+	if (test_and_clear_bit(WWAN_PORT_OPEN, &port->flags)) {
 		if (port->ops)
 			port->ops->stop(port);
 		skb_queue_purge(&port->rxq);
-- 
2.25.1