linux-kernel - [PATCH] usb: host: u132-hcd: Remove u132_static_list and list head u132

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Date:   Fri,  3 Apr 2020 23:48:16 +0530
From:   madhuparnabhowmik10@...il.com
To:     gregkh@...uxfoundation.org, hariprasad.kelam@...il.com,
        colin.king@...onical.com
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        ldv-project@...uxtesting.org, andrianov@...ras.ru,
        stern@...land.harvard.edu,
        Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>
Subject: [PATCH] usb: host: u132-hcd: Remove u132_static_list and list head u132_list

From: Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>

u132_static_list is a global list protected by u132_module_lock.
It is read in the u132_hcd_exit() function without holding the lock
thus may lead to data race.
However, it turns out that this list isn't used for anything useful
and thus it is okay to get rid of it.
Thus, remove the u132_static_list from u132-hcd module.
Also remove struct list_head u132_list from struct u132.

Found by Linux Driver Verification project (linuxtesting.org).

Suggested-by: Alan Stern <stern@...land.harvard.edu>
Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>
---
 drivers/usb/host/u132-hcd.c | 10 ----------
 1 file changed, 10 deletions(-)

diff --git a/drivers/usb/host/u132-hcd.c b/drivers/usb/host/u132-hcd.c
index e9209e3e6248..995bc52d2d22 100644
--- a/drivers/usb/host/u132-hcd.c
+++ b/drivers/usb/host/u132-hcd.c
@@ -81,7 +81,6 @@ static DECLARE_WAIT_QUEUE_HEAD(u132_hcd_wait);
 static struct mutex u132_module_lock;
 static int u132_exiting;
 static int u132_instances;
-static struct list_head u132_static_list;
 /*
 * end of the global variables protected by u132_module_lock
 */
@@ -177,7 +176,6 @@ struct u132_ring {
 };
 struct u132 {
 	struct kref kref;
-	struct list_head u132_list;
 	struct mutex sw_lock;
 	struct mutex scheduler_lock;
 	struct u132_platform_data *board;
@@ -254,7 +252,6 @@ static void u132_hcd_delete(struct kref *kref)
 	struct usb_hcd *hcd = u132_to_hcd(u132);
 	u132->going += 1;
 	mutex_lock(&u132_module_lock);
-	list_del_init(&u132->u132_list);
 	u132_instances -= 1;
 	mutex_unlock(&u132_module_lock);
 	dev_warn(&u132->platform_dev->dev, "FREEING the hcd=%p and thus the u13"
@@ -3089,7 +3086,6 @@ static int u132_probe(struct platform_device *pdev)
 		retval = 0;
 		hcd->rsrc_start = 0;
 		mutex_lock(&u132_module_lock);
-		list_add_tail(&u132->u132_list, &u132_static_list);
 		u132->sequence_num = ++u132_instances;
 		mutex_unlock(&u132_module_lock);
 		u132_u132_init_kref(u132);
@@ -3192,7 +3188,6 @@ static struct platform_driver u132_platform_driver = {
 static int __init u132_hcd_init(void)
 {
 	int retval;
-	INIT_LIST_HEAD(&u132_static_list);
 	u132_instances = 0;
 	u132_exiting = 0;
 	mutex_init(&u132_module_lock);
@@ -3213,14 +3208,9 @@ static int __init u132_hcd_init(void)
 module_init(u132_hcd_init);
 static void __exit u132_hcd_exit(void)
 {
-	struct u132 *u132;
-	struct u132 *temp;
 	mutex_lock(&u132_module_lock);
 	u132_exiting += 1;
 	mutex_unlock(&u132_module_lock);
-	list_for_each_entry_safe(u132, temp, &u132_static_list, u132_list) {
-		platform_device_unregister(u132->platform_dev);
-	}
 	platform_driver_unregister(&u132_platform_driver);
 	printk(KERN_INFO "u132-hcd driver deregistered\n");
 	wait_event(u132_hcd_wait, u132_instances == 0);
-- 
2.17.1