linux-kernel - Re: [PATCH v4] usb: gadget: udc: Handle gadget

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Date:   Wed, 27 Sep 2023 01:36:10 +0530
From:   Krishna Kurapati PSSNV <quic_kriskura@...cinc.com>
To:     Alan Stern <stern@...land.harvard.edu>
CC:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Francesco Dolcini <francesco.dolcini@...adex.com>,
        Badhri Jagan Sridharan <badhri@...gle.com>,
        Michael Grzeschik <m.grzeschik@...gutronix.de>,
        Ivan Orlov <ivan.orlov0322@...il.com>,
        <linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <quic_ppratap@...cinc.com>, <quic_wcheng@...cinc.com>,
        <quic_jackp@...cinc.com>
Subject: Re: [PATCH v4] usb: gadget: udc: Handle gadget_connect failure during
 bind operation



On 9/27/2023 1:24 AM, Alan Stern wrote:
> On Wed, Sep 27, 2023 at 01:07:08AM +0530, Krishna Kurapati wrote:
>> In the event, gadget_connect call (which invokes pullup) fails,
> 
> s/event,/event/
> 
>> propagate the error to udc bind operation which inturn sends the
> 
> s/inturn/in turn/
> 
>> error to configfs. The userspace can then retry enumeartion if
> 
> s/enumeartion/enumeration/
> 
>> it chooses to.
>>
>> Signed-off-by: Krishna Kurapati <quic_kriskura@...cinc.com>
>> ---
>> Changes in v4: Fixed mutex locking imbalance during connect_control
>> failure
>> Link to v3: https://lore.kernel.org/all/20230510075252.31023-3-quic_kriskura@quicinc.com/
>>
>>   drivers/usb/gadget/udc/core.c | 23 +++++++++++++++++++----
>>   1 file changed, 19 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/usb/gadget/udc/core.c b/drivers/usb/gadget/udc/core.c
>> index 7d49d8a0b00c..53af25a333a1 100644
>> --- a/drivers/usb/gadget/udc/core.c
>> +++ b/drivers/usb/gadget/udc/core.c
>> @@ -1125,12 +1125,16 @@ EXPORT_SYMBOL_GPL(usb_gadget_set_state);
>>   /* ------------------------------------------------------------------------- */
>>   
>>   /* Acquire connect_lock before calling this function. */
>> -static void usb_udc_connect_control_locked(struct usb_udc *udc) __must_hold(&udc->connect_lock)
>> +static int usb_udc_connect_control_locked(struct usb_udc *udc) __must_hold(&udc->connect_lock)
>>   {
>> +	int ret;
>> +
>>   	if (udc->vbus)
>> -		usb_gadget_connect_locked(udc->gadget);
>> +		ret = usb_gadget_connect_locked(udc->gadget);
>>   	else
>> -		usb_gadget_disconnect_locked(udc->gadget);
>> +		ret = usb_gadget_disconnect_locked(udc->gadget);
>> +
>> +	return ret;
> 
> You don't actually need the new variable ret.  You can just do:
> 
> 	if (udc->vbus)
> 		return usb_gadget_connect_locked(udc->gadget);
> 	else
> 		return usb_gadget_disconnect_locked(udc->gadget);
> 
>>   }
>>   
>>   static void vbus_event_work(struct work_struct *work)
>> @@ -1604,12 +1608,23 @@ static int gadget_bind_driver(struct device *dev)
>>   	}
>>   	usb_gadget_enable_async_callbacks(udc);
>>   	udc->allow_connect = true;
>> -	usb_udc_connect_control_locked(udc);
>> +	ret = usb_udc_connect_control_locked(udc);
>> +	if (ret) {
>> +		mutex_unlock(&udc->connect_lock);
>> +		goto err_connect_control;
>> +	}
>> +
>>   	mutex_unlock(&udc->connect_lock);
>>   
>>   	kobject_uevent(&udc->dev.kobj, KOBJ_CHANGE);
>>   	return 0;
>>   
>> + err_connect_control:
>> +	usb_gadget_disable_async_callbacks(udc);
>> +	if (gadget->irq)
>> +		synchronize_irq(gadget->irq);
>> +	usb_gadget_udc_stop_locked(udc);
> 
> Not good -- usb_gadget_udc_stop_locked() expects you to be holding
> udc->connect_lock, but you just dropped the lock!  Also, you never set
> udc->allow_connect back to false.
> 
> You should move the mutex_unlock() call from inside the "if" statement
> to down here, and add a line for udc->allow_connect.
> 

Hi Alan,

  Thanks for the review. Will push v5 addressing the changes.


Regards,
Krishna,