linux-kernel - [char-misc-next 2/4] mei: bus: make a client pointer always available

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Date:   Wed, 16 Nov 2016 22:51:28 +0200
From:   Tomas Winkler <tomas.winkler@...el.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Alexander Usyskin <alexander.usyskin@...el.com>,
        linux-kernel@...r.kernel.org,
        Tomas Winkler <tomas.winkler@...el.com>
Subject: [char-misc-next 2/4] mei: bus: make a client pointer always available

From: Alexander Usyskin <alexander.usyskin@...el.com>

Change life time of the client pointer, allocate it upon client device
creation and free it upon device destruction, instead of upon
connection and disconnection.
This helps to eliminate racy NULL checks in the bus code.

Signed-off-by: Alexander Usyskin <alexander.usyskin@...el.com>
Signed-off-by: Tomas Winkler <tomas.winkler@...el.com>
---
 drivers/misc/mei/bus.c | 31 +++++++++++++++----------------
 1 file changed, 15 insertions(+), 16 deletions(-)

diff --git a/drivers/misc/mei/bus.c b/drivers/misc/mei/bus.c
index 7c075e9b25e5..483587f60249 100644
--- a/drivers/misc/mei/bus.c
+++ b/drivers/misc/mei/bus.c
@@ -187,9 +187,6 @@ ssize_t mei_cldev_send(struct mei_cl_device *cldev, u8 *buf, size_t length)
 {
 	struct mei_cl *cl = cldev->cl;
 
-	if (cl == NULL)
-		return -ENODEV;
-
 	return __mei_cl_send(cl, buf, length, MEI_CL_IO_TX_BLOCKING);
 }
 EXPORT_SYMBOL_GPL(mei_cldev_send);
@@ -207,9 +204,6 @@ ssize_t mei_cldev_recv(struct mei_cl_device *cldev, u8 *buf, size_t length)
 {
 	struct mei_cl *cl = cldev->cl;
 
-	if (cl == NULL)
-		return -ENODEV;
-
 	return __mei_cl_recv(cl, buf, length);
 }
 EXPORT_SYMBOL_GPL(mei_cldev_recv);
@@ -403,7 +397,7 @@ EXPORT_SYMBOL_GPL(mei_cldev_ver);
  */
 bool mei_cldev_enabled(struct mei_cl_device *cldev)
 {
-	return cldev->cl && mei_cl_is_connected(cldev->cl);
+	return mei_cl_is_connected(cldev->cl);
 }
 EXPORT_SYMBOL_GPL(mei_cldev_enabled);
 
@@ -423,14 +417,13 @@ int mei_cldev_enable(struct mei_cl_device *cldev)
 
 	cl = cldev->cl;
 
-	if (!cl) {
+	if (cl->state == MEI_FILE_UNINITIALIZED) {
 		mutex_lock(&bus->device_lock);
-		cl = mei_cl_alloc_linked(bus);
+		ret = mei_cl_link(cl);
 		mutex_unlock(&bus->device_lock);
-		if (IS_ERR(cl))
-			return PTR_ERR(cl);
+		if (ret)
+			return ret;
 		/* update pointers */
-		cldev->cl = cl;
 		cl->cldev = cldev;
 	}
 
@@ -471,7 +464,7 @@ int mei_cldev_disable(struct mei_cl_device *cldev)
 	struct mei_cl *cl;
 	int err;
 
-	if (!cldev || !cldev->cl)
+	if (!cldev)
 		return -ENODEV;
 
 	cl = cldev->cl;
@@ -497,9 +490,6 @@ int mei_cldev_disable(struct mei_cl_device *cldev)
 	mei_cl_flush_queues(cl, NULL);
 	mei_cl_unlink(cl);
 
-	kfree(cl);
-	cldev->cl = NULL;
-
 	mutex_unlock(&bus->device_lock);
 	return err;
 }
@@ -754,6 +744,7 @@ static void mei_cl_bus_dev_release(struct device *dev)
 
 	mei_me_cl_put(cldev->me_cl);
 	mei_dev_bus_put(cldev->bus);
+	kfree(cldev->cl);
 	kfree(cldev);
 }
 
@@ -786,17 +777,25 @@ static struct mei_cl_device *mei_cl_bus_dev_alloc(struct mei_device *bus,
 						  struct mei_me_client *me_cl)
 {
 	struct mei_cl_device *cldev;
+	struct mei_cl *cl;
 
 	cldev = kzalloc(sizeof(struct mei_cl_device), GFP_KERNEL);
 	if (!cldev)
 		return NULL;
 
+	cl = mei_cl_allocate(bus);
+	if (!cl) {
+		kfree(cldev);
+		return NULL;
+	}
+
 	device_initialize(&cldev->dev);
 	cldev->dev.parent = bus->dev;
 	cldev->dev.bus    = &mei_cl_bus_type;
 	cldev->dev.type   = &mei_cl_device_type;
 	cldev->bus        = mei_dev_bus_get(bus);
 	cldev->me_cl      = mei_me_cl_get(me_cl);
+	cldev->cl         = cl;
 	mei_cl_bus_set_name(cldev);
 	cldev->is_added   = 0;
 	INIT_LIST_HEAD(&cldev->bus_list);
-- 
2.7.4