There can be multiple role switch devices running on a platform. Given
that lockdep is not capable of differentiating between locks of
different instances, false positive warnings for circular locking are
reported. To prevent this, register unique lockdep key for each of the
individual instances.

Signed-off-by: Amit Sunil Dhamne <amitsd@google.com>
---
 drivers/usb/roles/class.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/drivers/usb/roles/class.c b/drivers/usb/roles/class.c
index d7aa913ceb8a..807a8f18ec20 100644
--- a/drivers/usb/roles/class.c
+++ b/drivers/usb/roles/class.c
@@ -11,6 +11,7 @@
 #include <linux/usb/role.h>
 #include <linux/property.h>
 #include <linux/device.h>
+#include <linux/lockdep.h>
 #include <linux/module.h>
 #include <linux/mutex.h>
 #include <linux/slab.h>
@@ -33,6 +34,10 @@ struct usb_role_switch {
 	usb_role_switch_set_t set;
 	usb_role_switch_get_t get;
 	bool allow_userspace_control;
+
+#ifdef CONFIG_LOCKDEP
+	struct lock_class_key key;
+#endif
 };
 
 #define to_role_switch(d)	container_of(d, struct usb_role_switch, dev)
@@ -396,6 +401,11 @@ usb_role_switch_register(struct device *parent,
 
 	sw->registered = true;
 
+#ifdef CONFIG_LOCKDEP
+	lockdep_register_key(&sw->key);
+	lockdep_set_class(&sw->lock, &sw->key);
+#endif
+
 	/* TODO: Symlinks for the host port and the device controller. */
 
 	return sw;
@@ -412,6 +422,11 @@ void usb_role_switch_unregister(struct usb_role_switch *sw)
 {
 	if (IS_ERR_OR_NULL(sw))
 		return;
+
+#ifdef CONFIG_LOCKDEP
+	lockdep_unregister_key(&sw->key);
+#endif
+
 	sw->registered = false;
 	if (dev_fwnode(&sw->dev))
 		component_del(&sw->dev, &connector_ops);

base-commit: 38343be0bf9a7d7ef0d160da5f2db887a0e29b62
-- 
2.46.0.76.ge559c4bf1a-goog

On Tue, Aug 13, 2024 at 03:42:11PM -0700, Amit Sunil Dhamne wrote:
> There can be multiple role switch devices running on a platform. Given
> that lockdep is not capable of differentiating between locks of
> different instances, false positive warnings for circular locking are
> reported. To prevent this, register unique lockdep key for each of the
> individual instances.
> 
> Signed-off-by: Amit Sunil Dhamne <amitsd@google.com>
> ---
>  drivers/usb/roles/class.c | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/drivers/usb/roles/class.c b/drivers/usb/roles/class.c
> index d7aa913ceb8a..807a8f18ec20 100644
> --- a/drivers/usb/roles/class.c
> +++ b/drivers/usb/roles/class.c
> @@ -11,6 +11,7 @@
>  #include <linux/usb/role.h>
>  #include <linux/property.h>
>  #include <linux/device.h>
> +#include <linux/lockdep.h>
>  #include <linux/module.h>
>  #include <linux/mutex.h>
>  #include <linux/slab.h>
> @@ -33,6 +34,10 @@ struct usb_role_switch {
>  	usb_role_switch_set_t set;
>  	usb_role_switch_get_t get;
>  	bool allow_userspace_control;
> +
> +#ifdef CONFIG_LOCKDEP
> +	struct lock_class_key key;
> +#endif

Please do not put #ifdef lines in .c files, they are not needed for this
change to work properly, right?

checkpatch should have complained about this...

thanks,

greg k-h

On 8/13/24 9:49 PM, Greg KH wrote:
> On Tue, Aug 13, 2024 at 03:42:11PM -0700, Amit Sunil Dhamne wrote:
>> There can be multiple role switch devices running on a platform. Given
>> that lockdep is not capable of differentiating between locks of
>> different instances, false positive warnings for circular locking are
>> reported. To prevent this, register unique lockdep key for each of the
>> individual instances.
>>
>> Signed-off-by: Amit Sunil Dhamne <amitsd@google.com>
>> ---
>>   drivers/usb/roles/class.c | 15 +++++++++++++++
>>   1 file changed, 15 insertions(+)
>>
>> diff --git a/drivers/usb/roles/class.c b/drivers/usb/roles/class.c
>> index d7aa913ceb8a..807a8f18ec20 100644
>> --- a/drivers/usb/roles/class.c
>> +++ b/drivers/usb/roles/class.c
>> @@ -11,6 +11,7 @@
>>   #include <linux/usb/role.h>
>>   #include <linux/property.h>
>>   #include <linux/device.h>
>> +#include <linux/lockdep.h>
>>   #include <linux/module.h>
>>   #include <linux/mutex.h>
>>   #include <linux/slab.h>
>> @@ -33,6 +34,10 @@ struct usb_role_switch {
>>   	usb_role_switch_set_t set;
>>   	usb_role_switch_get_t get;
>>   	bool allow_userspace_control;
>> +
>> +#ifdef CONFIG_LOCKDEP
>> +	struct lock_class_key key;
>> +#endif
> Please do not put #ifdef lines in .c files, they are not needed for this
> change to work properly, right?
That's right. I will correct it in the next revision.
>
> checkpatch should have complained about this...

Unfortunately it didn't complain.

Thanks,

Amit

>
> thanks,
>
> greg k-h