linux-kernel - [PATCH v3 1/3] extcon: Use unique number for the extcon device ID

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Message-Id: <20230411114824.82960-2-andriy.shevchenko@linux.intel.com>
Date:   Tue, 11 Apr 2023 14:48:22 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Chanwoo Choi <cw00.choi@...sung.com>,
        Bumwoo Lee <bw365.lee@...sung.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        linux-kernel@...r.kernel.org
Cc:     MyungJoo Ham <myungjoo.ham@...sung.com>
Subject: [PATCH v3 1/3] extcon: Use unique number for the extcon device ID

The use of atomic variable is still racy when we do not control which
device has been unregistered and there is a (theoretical) possibility
of the overflow that may cause a duplicate extcon device ID number
to be allocated next time a device is registered.

Replace above mentioned approach by using IDA framework.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
---
 drivers/extcon/extcon.c | 16 +++++++++++++---
 drivers/extcon/extcon.h |  2 ++
 2 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/drivers/extcon/extcon.c b/drivers/extcon/extcon.c
index 47819c5144d5..5da1cc60582a 100644
--- a/drivers/extcon/extcon.c
+++ b/drivers/extcon/extcon.c
@@ -16,6 +16,7 @@
 
 #include <linux/module.h>
 #include <linux/types.h>
+#include <linux/idr.h>
 #include <linux/init.h>
 #include <linux/device.h>
 #include <linux/fs.h>
@@ -238,6 +239,7 @@ struct extcon_cable {
 
 static struct class *extcon_class;
 
+static DEFINE_IDA(extcon_dev_ids);
 static LIST_HEAD(extcon_dev_list);
 static DEFINE_MUTEX(extcon_dev_list_lock);
 
@@ -1248,7 +1250,6 @@ static int extcon_alloc_groups(struct extcon_dev *edev)
 int extcon_dev_register(struct extcon_dev *edev)
 {
 	int ret, index = 0;
-	static atomic_t edev_no = ATOMIC_INIT(-1);
 
 	ret = create_extcon_class();
 	if (ret < 0)
@@ -1275,8 +1276,14 @@ int extcon_dev_register(struct extcon_dev *edev)
 			"extcon device name is null\n");
 		return -EINVAL;
 	}
-	dev_set_name(&edev->dev, "extcon%lu",
-			(unsigned long)atomic_inc_return(&edev_no));
+
+	ret = ida_alloc(&extcon_dev_ids, GFP_KERNEL);
+	if (ret < 0)
+		return ret;
+
+	edev->id = ret;
+
+	dev_set_name(&edev->dev, "extcon%d", edev->id);
 
 	ret = extcon_alloc_cables(edev);
 	if (ret < 0)
@@ -1339,6 +1346,7 @@ int extcon_dev_register(struct extcon_dev *edev)
 	if (edev->max_supported)
 		kfree(edev->cables);
 err_alloc_cables:
+	ida_free(&extcon_dev_ids, edev->id);
 
 	return ret;
 }
@@ -1367,6 +1375,8 @@ void extcon_dev_unregister(struct extcon_dev *edev)
 		return;
 	}
 
+	ida_free(&extcon_dev_ids, edev->id);
+
 	device_unregister(&edev->dev);
 
 	if (edev->mutually_exclusive && edev->max_supported) {
diff --git a/drivers/extcon/extcon.h b/drivers/extcon/extcon.h
index 15616446140d..946182687786 100644
--- a/drivers/extcon/extcon.h
+++ b/drivers/extcon/extcon.h
@@ -20,6 +20,7 @@
  *			{0x3, 0x6, 0x5, 0}. If it is {0xFFFFFFFF, 0}, there
  *			can be no simultaneous connections.
  * @dev:		Device of this extcon.
+ * @id:			Unique device ID of this extcon.
  * @state:		Attach/detach state of this extcon. Do not provide at
  *			register-time.
  * @nh_all:		Notifier for the state change events for all supported
@@ -46,6 +47,7 @@ struct extcon_dev {
 
 	/* Internal data. Please do not set. */
 	struct device dev;
+	unsigned int id;
 	struct raw_notifier_head nh_all;
 	struct raw_notifier_head *nh;
 	struct list_head entry;
-- 
2.40.0.1.gaa8946217a0b