Re: [PATCH 1/1] usb: gadget: Don't attempt to dequeue requests fora disabled USB endpoint on Freescale hardware

[Simon Haggett]

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@xxxxxxxxxxx>
> > > > ---
> > > >
> > > >   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

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/