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

From: Simon Haggett
Date: Mon Oct 22 2012 - 07:59:52 EST


On 22/10/12 11:47, Laurent Pinchart wrote:

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

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


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
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


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