platform/chrome: cros_ec_rpmsg: Fix race with host command when probe failed

Since the rpmsg_endpoint is created before probe is called, it's
possible that a host event is received during cros_ec_register, and
there would be some pending work in the host_event_work workqueue while
cros_ec_register is called.

If cros_ec_register fails, when the leftover work in host_event_work
run, the ec_dev from the drvdata of the rpdev could be already set to
NULL, causing kernel crash when trying to run cros_ec_get_next_event.

Fix this by creating the rpmsg_endpoint by ourself, and when
cros_ec_register fails (or on remove), destroy the endpoint first (to
make sure there's no more new calls to cros_ec_rpmsg_callback), and then
cancel all works in the host_event_work workqueue.

Cc: stable@vger.kernel.org
Fixes: 2de89fd9 ("platform/chrome: cros_ec: Add EC host command support using rpmsg")
Signed-off-by: Pi-Hsun Shih <pihsun@chromium.org>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>

drivers/platform/chrome/cros_ec_rpmsg.c

@@ -41,6 +41,7 @@ struct cros_ec_rpmsg {
 	struct rpmsg_device *rpdev;
 	struct completion xfer_ack;
 	struct work_struct host_event_work;
+	struct rpmsg_endpoint *ept;
 };
 
 /**
@@ -72,7 +73,6 @@ static int cros_ec_pkt_xfer_rpmsg(struct cros_ec_device *ec_dev,
 				  struct cros_ec_command *ec_msg)
 {
 	struct cros_ec_rpmsg *ec_rpmsg = ec_dev->priv;
-	struct rpmsg_device *rpdev = ec_rpmsg->rpdev;
 	struct ec_host_response *response;
 	unsigned long timeout;
 	int len;
@@ -85,7 +85,7 @@ static int cros_ec_pkt_xfer_rpmsg(struct cros_ec_device *ec_dev,
 	dev_dbg(ec_dev->dev, "prepared, len=%d\n", len);
 
 	reinit_completion(&ec_rpmsg->xfer_ack);
-	ret = rpmsg_send(rpdev->ept, ec_dev->dout, len);
+	ret = rpmsg_send(ec_rpmsg->ept, ec_dev->dout, len);
 	if (ret) {
 		dev_err(ec_dev->dev, "rpmsg send failed\n");
 		return ret;
@@ -196,11 +196,24 @@ static int cros_ec_rpmsg_callback(struct rpmsg_device *rpdev, void *data,
 	return 0;
 }
 
+static struct rpmsg_endpoint *
+cros_ec_rpmsg_create_ept(struct rpmsg_device *rpdev)
+{
+	struct rpmsg_channel_info chinfo = {};
+
+	strscpy(chinfo.name, rpdev->id.name, RPMSG_NAME_SIZE);
+	chinfo.src = rpdev->src;
+	chinfo.dst = RPMSG_ADDR_ANY;
+
+	return rpmsg_create_ept(rpdev, cros_ec_rpmsg_callback, NULL, chinfo);
+}
+
 static int cros_ec_rpmsg_probe(struct rpmsg_device *rpdev)
 {
 	struct device *dev = &rpdev->dev;
 	struct cros_ec_rpmsg *ec_rpmsg;
 	struct cros_ec_device *ec_dev;
+	int ret;
 
 	ec_dev = devm_kzalloc(dev, sizeof(*ec_dev), GFP_KERNEL);
 	if (!ec_dev)
@@ -225,7 +238,18 @@ static int cros_ec_rpmsg_probe(struct rpmsg_device *rpdev)
 	INIT_WORK(&ec_rpmsg->host_event_work,
 		  cros_ec_rpmsg_host_event_function);
 
-	return cros_ec_register(ec_dev);
+	ec_rpmsg->ept = cros_ec_rpmsg_create_ept(rpdev);
+	if (!ec_rpmsg->ept)
+		return -ENOMEM;
+
+	ret = cros_ec_register(ec_dev);
+	if (ret < 0) {
+		rpmsg_destroy_ept(ec_rpmsg->ept);
+		cancel_work_sync(&ec_rpmsg->host_event_work);
+		return ret;
+	}
+
+	return 0;
 }
 
 static void cros_ec_rpmsg_remove(struct rpmsg_device *rpdev)
@@ -234,7 +258,7 @@ static void cros_ec_rpmsg_remove(struct rpmsg_device *rpdev)
 	struct cros_ec_rpmsg *ec_rpmsg = ec_dev->priv;
 
 	cros_ec_unregister(ec_dev);
-
+	rpmsg_destroy_ept(ec_rpmsg->ept);
 	cancel_work_sync(&ec_rpmsg->host_event_work);
 }
 
@@ -271,7 +295,6 @@ static struct rpmsg_driver cros_ec_driver_rpmsg = {
 	},
 	.probe		= cros_ec_rpmsg_probe,
 	.remove		= cros_ec_rpmsg_remove,
-	.callback	= cros_ec_rpmsg_callback,
 };
 
 module_rpmsg_driver(cros_ec_driver_rpmsg);