netdev - [PATCH net-next 1/2] net: wwan: debugfs obtained dev reference not dropped

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Message-Id: <20220214071653.813010-2-m.chetan.kumar@linux.intel.com>
Date:   Mon, 14 Feb 2022 12:46:52 +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-next 1/2] net: wwan: debugfs obtained dev reference not dropped

WWAN driver call's wwan_get_debugfs_dir() to obtain
WWAN debugfs dir entry. As part of this procedure it
returns a reference to a found device.

Since there is no debugfs interface available at WWAN
subsystem, it is not possible to drop dev reference post
debugfs use. This leads to side effects like post wwan
driver load and reload the wwan instance gets increment
from wwanX to wwanX+1.

A new debugfs interface is added in wwan subsystem so that
wwan driver can drop the obtained dev reference post debugfs
use.

void wwan_put_debugfs_dir(struct dentry *dir)

Signed-off-by: M Chetan Kumar <m.chetan.kumar@...ux.intel.com>
---
 drivers/net/wwan/wwan_core.c | 35 +++++++++++++++++++++++++++++++++++
 include/linux/wwan.h         |  2 ++
 2 files changed, 37 insertions(+)

diff --git a/drivers/net/wwan/wwan_core.c b/drivers/net/wwan/wwan_core.c
index 1508dc2a497b..147b88464cbd 100644
--- a/drivers/net/wwan/wwan_core.c
+++ b/drivers/net/wwan/wwan_core.c
@@ -160,6 +160,42 @@ struct dentry *wwan_get_debugfs_dir(struct device *parent)
 	return wwandev->debugfs_dir;
 }
 EXPORT_SYMBOL_GPL(wwan_get_debugfs_dir);
+
+static int wwan_dev_debugfs_match(struct device *dev, const void *dir)
+{
+	struct wwan_device *wwandev;
+
+	if (dev->type != &wwan_dev_type)
+		return 0;
+
+	wwandev = to_wwan_dev(dev);
+
+	return wwandev->debugfs_dir == dir;
+}
+
+static struct wwan_device *wwan_dev_get_by_debugfs(struct dentry *dir)
+{
+	struct device *dev;
+
+	dev = class_find_device(wwan_class, NULL, dir, wwan_dev_debugfs_match);
+	if (!dev)
+		return ERR_PTR(-ENODEV);
+
+	return to_wwan_dev(dev);
+}
+
+void wwan_put_debugfs_dir(struct dentry *dir)
+{
+	struct wwan_device *wwandev = wwan_dev_get_by_debugfs(dir);
+
+	if (WARN_ON(IS_ERR(wwandev)))
+		return;
+
+	/* wwan_dev_get_by_debugfs() also got a reference */
+	put_device(&wwandev->dev);
+	put_device(&wwandev->dev);
+}
+EXPORT_SYMBOL_GPL(wwan_put_debugfs_dir);
 #endif
 
 /* This function allocates and registers a new WWAN device OR if a WWAN device
diff --git a/include/linux/wwan.h b/include/linux/wwan.h
index afb3334ec8c5..5ce2acf444fb 100644
--- a/include/linux/wwan.h
+++ b/include/linux/wwan.h
@@ -174,11 +174,13 @@ void wwan_unregister_ops(struct device *parent);
 
 #ifdef CONFIG_WWAN_DEBUGFS
 struct dentry *wwan_get_debugfs_dir(struct device *parent);
+void wwan_put_debugfs_dir(struct dentry *dir);
 #else
 static inline struct dentry *wwan_get_debugfs_dir(struct device *parent)
 {
 	return ERR_PTR(-ENODEV);
 }
+static inline void wwan_put_debugfs_dir(struct dentry *dir) {}
 #endif
 
 #endif /* __WWAN_H */
-- 
2.25.1