Subject: Re: [PATCH 2/6 v3] usb/fsl_qe_udc: Fix recursive locking bug in ch9getstatus()

From: David Brownell <[email-masked]>
Date: Wed, 19 Nov 2008 21:41:36 -0800

On Tuesday 18 November 2008, Anton Vorontsov wrote:
> The call chain is this:
> 
> qe_udc_irq() <- grabs the udc->lock spinlock
> rx_irq()
> qe_ep0_rx()
> ep0_setup_handle()
> setup_received_handle()
> ch9getstatus()
> qe_ep_queue() <- tries to grab the udc->lock again
> 
> It seems unsafe to temporarily drop the lock in the ch9getstatus(),
> so to fix that bug the lock-less __qe_ep_queue() function
> implemented and used by the ch9getstatus().
> 
> Signed-off-by: Anton Vorontsov <[email-masked]>

Acked-by: David Brownell <[email-masked]>

... noting that this *also* fixes a locking bug in qe_ep_queue(),
where it modified the queue head without holding the spinlock.

(So for example an IRQ in the middle of that update could end
up updating the incompletely updated list head ... oopsie!)

And I'd have made the __qe_ep_queue() routine take a qe_ep
and qe_req, but that's just a minor issue.

> ---
> 
> On Tue, Nov 18, 2008 at 02:13:30PM -0800, David Brownell wrote:
> > On Tuesday 18 November 2008, Anton Vorontsov wrote:
> > > +       spin_lock_irqsave(&udc->lock, flags);
> > > +       ret = __qe_ep_queue(_ep, _req, gfp_flags);
> > > +       spin_unlock_irqrestore(&udc->lock, flags);
> > 
> > Why are you passing "gfp_flags"?  Especially without
> > checking ... GFP_KERNEL will be illegal, for example.
> 
> Ugh, the gfp_flags aren't used at all. How about that
> patch?
> 
>  drivers/usb/gadget/fsl_qe_udc.c |   26 ++++++++++++++++++--------
>  1 files changed, 18 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/usb/gadget/fsl_qe_udc.c b/drivers/usb/gadget/fsl_qe_udc.c
> index 60b9279..3587970 100644
> --- a/drivers/usb/gadget/fsl_qe_udc.c
> +++ b/drivers/usb/gadget/fsl_qe_udc.c
> @@ -1681,14 +1681,11 @@ static void qe_free_request(struct usb_ep *_ep, struct usb_request *_req)
>  		kfree(req);
>  }
>  
> -/* queues (submits) an I/O request to an endpoint */
> -static int qe_ep_queue(struct usb_ep *_ep, struct usb_request *_req,
> -				gfp_t gfp_flags)
> +static int __qe_ep_queue(struct usb_ep *_ep, struct usb_request *_req)
>  {
>  	struct qe_ep *ep = container_of(_ep, struct qe_ep, ep);
>  	struct qe_req *req = container_of(_req, struct qe_req, req);
>  	struct qe_udc *udc;
> -	unsigned long flags;
>  	int reval;
>  
>  	udc = ep->udc;
> @@ -1732,7 +1729,7 @@ static int qe_ep_queue(struct usb_ep *_ep, struct usb_request *_req,
>  	list_add_tail(&req->queue, &ep->queue);
>  	dev_vdbg(udc->dev, "gadget have request in %s! %d\n",
>  			ep->name, req->req.length);
> -	spin_lock_irqsave(&udc->lock, flags);
> +
>  	/* push the request to device */
>  	if (ep_is_in(ep))
>  		reval = ep_req_send(ep, req);
> @@ -1748,11 +1745,24 @@ static int qe_ep_queue(struct usb_ep *_ep, struct usb_request *_req,
>  	if (ep->dir == USB_DIR_OUT)
>  		reval = ep_req_receive(ep, req);
>  
> -	spin_unlock_irqrestore(&udc->lock, flags);
> -
>  	return 0;
>  }
>  
> +/* queues (submits) an I/O request to an endpoint */
> +static int qe_ep_queue(struct usb_ep *_ep, struct usb_request *_req,
> +		       gfp_t gfp_flags)
> +{
> +	struct qe_ep *ep = container_of(_ep, struct qe_ep, ep);
> +	struct qe_udc *udc = ep->udc;
> +	unsigned long flags;
> +	int ret;
> +
> +	spin_lock_irqsave(&udc->lock, flags);
> +	ret = __qe_ep_queue(_ep, _req);
> +	spin_unlock_irqrestore(&udc->lock, flags);
> +	return ret;
> +}
> +
>  /* dequeues (cancels, unlinks) an I/O request from an endpoint */
>  static int qe_ep_dequeue(struct usb_ep *_ep, struct usb_request *_req)
>  {
> @@ -2008,7 +2018,7 @@ static void ch9getstatus(struct qe_udc *udc, u8 request_type, u16 value,
>  	udc->ep0_dir = USB_DIR_IN;
>  
>  	/* data phase */
> -	status = qe_ep_queue(&ep->ep, &req->req, GFP_ATOMIC);
> +	status = __qe_ep_queue(&ep->ep, &req->req);
>  
>  	if (status == 0)
>  		return;
> -- 
> 1.5.6.3
> 
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