[PATCH] usb: host: u132-hcd: Remove u132_static_list

[PATCH] usb: host: u132-hcd: Remove u132_static_list

[madhuparnabhowmik10]

From: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.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.

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

Suggested-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
---
 drivers/usb/host/u132-hcd.c | 8 --------
 1 file changed, 8 deletions(-)

diff --git a/drivers/usb/host/u132-hcd.c b/drivers/usb/host/u132-hcd.c
index e9209e3e6248..52f70cf063ea 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
 */
@@ -3089,7 +3088,6 @@ 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 +3190,6 @@ 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 +3210,9 @@ 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

Re: [PATCH] usb: host: u132-hcd: Remove u132_static_list

[Alan Stern]

On Fri, 3 Apr 2020 madhuparnabhowmik10@gmail.com wrote:

> From: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.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.
> 
> Found by Linux Driver Verification project (linuxtesting.org).
> 
> Suggested-by: Alan Stern <stern@rowland.harvard.edu>
> Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
> ---
>  drivers/usb/host/u132-hcd.c | 8 --------
>  1 file changed, 8 deletions(-)
> 
> diff --git a/drivers/usb/host/u132-hcd.c b/drivers/usb/host/u132-hcd.c
> index e9209e3e6248..52f70cf063ea 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
>  */

You forgot to remove the u132_list member from struct u132.

Alan Stern

Re: [PATCH] usb: host: u132-hcd: Remove u132_static_list

[Madhuparna Bhowmik]

On Fri, Apr 03, 2020 at 10:39:33AM -0400, Alan Stern wrote:
> On Fri, 3 Apr 2020 madhuparnabhowmik10@gmail.com wrote:
> 
> > From: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.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.
> > 
> > Found by Linux Driver Verification project (linuxtesting.org).
> > 
> > Suggested-by: Alan Stern <stern@rowland.harvard.edu>
> > Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
> > ---
> >  drivers/usb/host/u132-hcd.c | 8 --------
> >  1 file changed, 8 deletions(-)
> > 
> > diff --git a/drivers/usb/host/u132-hcd.c b/drivers/usb/host/u132-hcd.c
> > index e9209e3e6248..52f70cf063ea 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
> >  */
> 
> You forgot to remove the u132_list member from struct u132.
>
Thank you for letting me know, I will send the patch again with this
change.

Regards,
Madhuparna

> Alan Stern
>