linux-kernel - Re: [PATCH 1/1] usb: gadget: Don't attempt to dequeue requests for a disabled USB endpoint on Freescale hardware

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Date:	Mon, 22 Oct 2012 12:49:51 +0100
From:	Simon Haggett <simon.haggett@...lvnc.com>
To:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
CC:	Li Yang-R58472 <r58472@...escale.com>,
	"balbi@...com" <balbi@...com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] usb: gadget: Don't attempt to dequeue requests for
 a disabled USB endpoint on Freescale hardware

Hi

On 22/10/12 11:47, Laurent Pinchart wrote:
> Hi,
>
> On Monday 22 October 2012 03:33:19 Li Yang-R58472 wrote:
>> On Saturday, October 20, 2012 1:37 AM Felipe Balbi wrote:
>>> On Fri, Oct 19, 2012 at 06:19:26PM +0100, Simon Haggett wrote:
>>>> Some gadget drivers may attempt to dequeue requests for an endpoint
>>>> that has already been disabled. For example, in the UVC gadget driver,
>>>> uvc_function_set_alt() will call usb_ep_disable() when alt setting 0
>>>> is selected. When the userspace application subsequently issues the
>>>> VIDIOC_STREAMOFF ioctl, uvc_video_enable() invokes usb_ep_dequeue() to
>>>
>>> ensure that all requests have been cancelled.
>>>
>>> bug is on uvc gadget, then. Laurent ?
>
> We've discussed this topic a couple of months before. I believe that's not a
> bug.
>
> http://68.183.106.108/lists/linux-usb/msg68869.html
>
>>> Also, fsl should be removed from the tree, I'm trying to persuade iMX
>>> folks to use drivers/usb/chipidea instead.
>>
>> Besides the iMX usage, the driver is also being used by many Freescale
>> PowerPC/Coldfire SoCs.  I agree that it's ideal to move to a common driver.
>> But it is a large task to make the chipidea driver works for all the
>> hardware that fsl_udc had supported and been tested on.
>>
>>>> For the Freescale High Speed Dual-Role USB controller,
>>>> fsl_ep_dequeue() provides the implementation of usb_ep_dequeue(). If
>>>> this is called for a disabled endpoint, a kernel oops will occur when
>>>
>>> the ep->ep.desc field is dereferenced (by ep_index()).
>>>
>>>> fsl_ep_disable() sets this field to NULL, as well as deleting all
>>>> pending requests for the endpoint.
>>>>
>>>> This patch adds an additional check to fsl_ep_dequeue() to ensure that
>>>> the endpoint has not already been disabled before attempting to dequeue
>>>
>>> requests.
>>>
>>>> Signed-off-by: Simon Haggett <simon.haggett@...lvnc.com>
>>>> ---
>>>>
>>>>   drivers/usb/gadget/fsl_udc_core.c |    5 ++++-
>>>>   1 files changed, 4 insertions(+), 1 deletions(-)
>>>>
>>>> diff --git a/drivers/usb/gadget/fsl_udc_core.c
>>>> b/drivers/usb/gadget/fsl_udc_core.c
>>>> index 6ae70cb..acd513b 100644
>>>> --- a/drivers/usb/gadget/fsl_udc_core.c
>>>> +++ b/drivers/usb/gadget/fsl_udc_core.c
>>>> @@ -955,7 +955,10 @@ static int fsl_ep_dequeue(struct usb_ep *_ep,
>>> struct usb_request *_req)
>>>
>>>>   	int ep_num, stopped, ret = 0;
>>>>   	u32 epctrl;
>>>>
>>>> -	if (!_ep || !_req)
>>>> +	/* Ensure that the ep and request are valid, and the ep is not
>>>> +	 * disabled
>>>> +	 */
>>>> +	if (!_ep || !_req || !ep->ep.desc)
>>>>   		return -EINVAL;
>
> Shouldn't that last check be done with a lock taken ?

I had presumed a lock wasn't necessary because ep->ep.desc is only set 
to NULL by fsl_ep_disable() which, since it is called by 
usb_ep_disable(), should only be invoked when no other task is using the 
endpoint (according to include/linux/usb/gadget.h). Furthermore, the 
chipidea UDC driver does check the equivalent of this field is not NULL 
without taking a lock (ep_dequeue() in drivers/usb/chipidea/udc.c).

However, it is possible that I'm misunderstanding something here, so 
apologies if I am.

>
>>>>   	spin_lock_irqsave(&ep->udc->lock, flags);
>

Many thanks

Simon

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