USB: separate out endpoint queue management and DMA mapping routines

This patch (as953) separates out three key portions from
usb_hcd_submit_urb(), usb_hcd_unlink_urb(), and usb_hcd_giveback_urb()
and puts them in separate functions of their own.  In the next patch,
these functions will be called directly by host controller drivers
while holding their private spinlocks, which will remove the
possibility of some unpleasant races.

The code responsible for mapping and unmapping DMA buffers is also
placed into a couple of separate subroutines, for the sake of
cleanliness and consistency.
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/core/hcd.c

@@ -914,99 +914,117 @@ EXPORT_SYMBOL (usb_calc_bus_time);
 
 /*-------------------------------------------------------------------------*/
 
-static void urb_unlink(struct usb_hcd *hcd, struct urb *urb)
+static int usb_hcd_link_urb_to_ep(struct usb_hcd *hcd, struct urb *urb)
 {
-	unsigned long		flags;
+	unsigned long	flags;
+	int		rc = 0;
 
-	/* clear all state linking urb to this dev (and hcd) */
 	spin_lock_irqsave(&hcd_urb_list_lock, flags);
-	list_del_init (&urb->urb_list);
-	spin_unlock_irqrestore(&hcd_urb_list_lock, flags);
 
-	if (hcd->self.uses_dma && !is_root_hub(urb->dev)) {
-		if (usb_endpoint_xfer_control(&urb->ep->desc)
-			&& !(urb->transfer_flags & URB_NO_SETUP_DMA_MAP))
-			dma_unmap_single (hcd->self.controller, urb->setup_dma,
-					sizeof (struct usb_ctrlrequest),
-					DMA_TO_DEVICE);
-		if (urb->transfer_buffer_length != 0
-			&& !(urb->transfer_flags & URB_NO_TRANSFER_DMA_MAP))
-			dma_unmap_single (hcd->self.controller,
-					urb->transfer_dma,
-					urb->transfer_buffer_length,
-					usb_urb_dir_in(urb)
-					    ? DMA_FROM_DEVICE
-					    : DMA_TO_DEVICE);
+	/* Check that the URB isn't being killed */
+	if (unlikely(urb->reject)) {
+		rc = -EPERM;
+		goto done;
 	}
-}
-
-/* may be called in any context with a valid urb->dev usecount
- * caller surrenders "ownership" of urb
- * expects usb_submit_urb() to have sanity checked and conditioned all
- * inputs in the urb
- */
-int usb_hcd_submit_urb (struct urb *urb, gfp_t mem_flags)
-{
-	int			status;
-	struct usb_hcd		*hcd = bus_to_hcd(urb->dev->bus);
-	unsigned long		flags;
-
-	if (!hcd)
-		return -ENODEV;
 
-	usbmon_urb_submit(&hcd->self, urb);
+	if (unlikely(!urb->ep->enabled)) {
+		rc = -ENOENT;
+		goto done;
+	}
 
 	/*
-	 * Atomically queue the urb,  first to our records, then to the HCD.
-	 * Access to urb->status is controlled by urb->lock ... changes on
-	 * i/o completion (normal or fault) or unlinking.
+	 * Check the host controller's state and add the URB to the
+	 * endpoint's queue.
 	 */
-
-	// FIXME:  verify that quiescing hc works right (RH cleans up)
-
-	spin_lock_irqsave(&hcd_urb_list_lock, flags);
-	if (unlikely(!urb->ep->enabled))
-		status = -ENOENT;
-	else if (unlikely (urb->reject))
-		status = -EPERM;
-	else switch (hcd->state) {
+	switch (hcd->state) {
 	case HC_STATE_RUNNING:
 	case HC_STATE_RESUMING:
-		list_add_tail (&urb->urb_list, &urb->ep->urb_list);
-		status = 0;
+		list_add_tail(&urb->urb_list, &urb->ep->urb_list);
 		break;
 	default:
-		status = -ESHUTDOWN;
-		break;
+		rc = -ESHUTDOWN;
+		goto done;
 	}
+ done:
 	spin_unlock_irqrestore(&hcd_urb_list_lock, flags);
-	if (status) {
-		INIT_LIST_HEAD (&urb->urb_list);
-		usbmon_urb_submit_error(&hcd->self, urb, status);
-		return status;
+	return rc;
+}
+
+static int usb_hcd_check_unlink_urb(struct usb_hcd *hcd, struct urb *urb,
+		int status)
+{
+	unsigned long		flags;
+	struct list_head	*tmp;
+	int			rc = 0;
+
+	/*
+	 * we contend for urb->status with the hcd core,
+	 * which changes it while returning the urb.
+	 *
+	 * Caller guaranteed that the urb pointer hasn't been freed, and
+	 * that it was submitted.  But as a rule it can't know whether or
+	 * not it's already been unlinked ... so we respect the reversed
+	 * lock sequence needed for the usb_hcd_giveback_urb() code paths
+	 * (urb lock, then hcd_urb_list_lock) in case some other CPU is now
+	 * unlinking it.
+	 */
+	spin_lock_irqsave(&urb->lock, flags);
+	spin_lock(&hcd_urb_list_lock);
+
+	/* insist the urb is still queued */
+	list_for_each(tmp, &urb->ep->urb_list) {
+		if (tmp == &urb->urb_list)
+			break;
+	}
+	if (tmp != &urb->urb_list) {
+		rc = -EIDRM;
+		goto done;
 	}
 
-	/* increment urb's reference count as part of giving it to the HCD
-	 * (which now controls it).  HCD guarantees that it either returns
-	 * an error or calls giveback(), but not both.
+	/* Any status except -EINPROGRESS means something already started to
+	 * unlink this URB from the hardware.  So there's no more work to do.
 	 */
-	urb = usb_get_urb (urb);
-	atomic_inc (&urb->use_count);
-
-	if (is_root_hub(urb->dev)) {
-		/* NOTE:  requirement on hub callers (usbfs and the hub
-		 * driver, for now) that URBs' urb->transfer_buffer be
-		 * valid and usb_buffer_{sync,unmap}() not be needed, since
-		 * they could clobber root hub response data.
-		 */
-		status = rh_urb_enqueue (hcd, urb);
+	if (urb->status != -EINPROGRESS) {
+		rc = -EBUSY;
 		goto done;
 	}
+	urb->status = status;
+
+	/* IRQ setup can easily be broken so that USB controllers
+	 * never get completion IRQs ... maybe even the ones we need to
+	 * finish unlinking the initial failed usb_set_address()
+	 * or device descriptor fetch.
+	 */
+	if (!test_bit(HCD_FLAG_SAW_IRQ, &hcd->flags) &&
+			!is_root_hub(urb->dev)) {
+		dev_warn(hcd->self.controller, "Unlink after no-IRQ?  "
+			"Controller is probably using the wrong IRQ.\n");
+		set_bit(HCD_FLAG_SAW_IRQ, &hcd->flags);
+	}
+
+ done:
+	spin_unlock(&hcd_urb_list_lock);
+	spin_unlock_irqrestore (&urb->lock, flags);
+	return rc;
+}
+
+static void usb_hcd_unlink_urb_from_ep(struct usb_hcd *hcd, struct urb *urb)
+{
+	unsigned long		flags;
 
-	/* lower level hcd code should use *_dma exclusively,
+	/* clear all state linking urb to this dev (and hcd) */
+	spin_lock_irqsave(&hcd_urb_list_lock, flags);
+	list_del_init(&urb->urb_list);
+	spin_unlock_irqrestore(&hcd_urb_list_lock, flags);
+}
+
+static void map_urb_for_dma(struct usb_hcd *hcd, struct urb *urb)
+{
+	/* Map the URB's buffers for DMA access.
+	 * Lower level HCD code should use *_dma exclusively,
 	 * unless it uses pio or talks to another transport.
 	 */
-	if (hcd->self.uses_dma) {
+	if (hcd->self.uses_dma && !is_root_hub(urb->dev)) {
 		if (usb_endpoint_xfer_control(&urb->ep->desc)
 			&& !(urb->transfer_flags & URB_NO_SETUP_DMA_MAP))
 			urb->setup_dma = dma_map_single (
@@ -1024,16 +1042,73 @@ int usb_hcd_submit_urb (struct urb *urb, gfp_t mem_flags)
 					    ? DMA_FROM_DEVICE
 					    : DMA_TO_DEVICE);
 	}
+}
 
-	status = hcd->driver->urb_enqueue (hcd, urb->ep, urb, mem_flags);
-done:
-	if (unlikely (status)) {
-		urb_unlink(hcd, urb);
-		atomic_dec (&urb->use_count);
-		if (urb->reject)
-			wake_up (&usb_kill_urb_queue);
+static void unmap_urb_for_dma(struct usb_hcd *hcd, struct urb *urb)
+{
+	if (hcd->self.uses_dma && !is_root_hub(urb->dev)) {
+		if (usb_endpoint_xfer_control(&urb->ep->desc)
+			&& !(urb->transfer_flags & URB_NO_SETUP_DMA_MAP))
+			dma_unmap_single(hcd->self.controller, urb->setup_dma,
+					sizeof(struct usb_ctrlrequest),
+					DMA_TO_DEVICE);
+		if (urb->transfer_buffer_length != 0
+			&& !(urb->transfer_flags & URB_NO_TRANSFER_DMA_MAP))
+			dma_unmap_single(hcd->self.controller,
+					urb->transfer_dma,
+					urb->transfer_buffer_length,
+					usb_urb_dir_in(urb)
+					    ? DMA_FROM_DEVICE
+					    : DMA_TO_DEVICE);
+	}
+}
+
+/*-------------------------------------------------------------------------*/
+
+/* may be called in any context with a valid urb->dev usecount
+ * caller surrenders "ownership" of urb
+ * expects usb_submit_urb() to have sanity checked and conditioned all
+ * inputs in the urb
+ */
+int usb_hcd_submit_urb (struct urb *urb, gfp_t mem_flags)
+{
+	int			status;
+	struct usb_hcd		*hcd = bus_to_hcd(urb->dev->bus);
+
+	/* increment urb's reference count as part of giving it to the HCD
+	 * (which will control it).  HCD guarantees that it either returns
+	 * an error or calls giveback(), but not both.
+	 */
+	usb_get_urb(urb);
+	atomic_inc(&urb->use_count);
+	usbmon_urb_submit(&hcd->self, urb);
+
+	/* NOTE requirements on root-hub callers (usbfs and the hub
+	 * driver, for now):  URBs' urb->transfer_buffer must be
+	 * valid and usb_buffer_{sync,unmap}() not be needed, since
+	 * they could clobber root hub response data.  Also, control
+	 * URBs must be submitted in process context with interrupts
+	 * enabled.
+	 */
+	status = usb_hcd_link_urb_to_ep(hcd, urb);
+	if (!status) {
+		map_urb_for_dma(hcd, urb);
+		if (is_root_hub(urb->dev))
+			status = rh_urb_enqueue(hcd, urb);
+		else
+			status = hcd->driver->urb_enqueue(hcd, urb->ep, urb,
+					mem_flags);
+	}
+
+	if (unlikely(status)) {
 		usbmon_urb_submit_error(&hcd->self, urb, status);
-		usb_put_urb (urb);
+		unmap_urb_for_dma(hcd, urb);
+		usb_hcd_unlink_urb_from_ep(hcd, urb);
+		INIT_LIST_HEAD(&urb->urb_list);
+		atomic_dec(&urb->use_count);
+		if (urb->reject)
+			wake_up(&usb_kill_urb_queue);
+		usb_put_urb(urb);
 	}
 	return status;
 }
@@ -1074,78 +1149,20 @@ unlink1 (struct usb_hcd *hcd, struct urb *urb)
  */
 int usb_hcd_unlink_urb (struct urb *urb, int status)
 {
-	struct usb_hcd			*hcd = NULL;
-	struct device			*sys = NULL;
-	unsigned long			flags;
-	struct list_head		*tmp;
-	int				retval;
-
-	/*
-	 * we contend for urb->status with the hcd core,
-	 * which changes it while returning the urb.
-	 *
-	 * Caller guaranteed that the urb pointer hasn't been freed, and
-	 * that it was submitted.  But as a rule it can't know whether or
-	 * not it's already been unlinked ... so we respect the reversed
-	 * lock sequence needed for the usb_hcd_giveback_urb() code paths
-	 * (urb lock, then hcd_urb_list_lock) in case some other CPU is now
-	 * unlinking it.
-	 */
-	spin_lock_irqsave (&urb->lock, flags);
-	spin_lock(&hcd_urb_list_lock);
+	struct usb_hcd		*hcd;
+	int			retval;
 
-	sys = &urb->dev->dev;
 	hcd = bus_to_hcd(urb->dev->bus);
-	if (hcd == NULL) {
-		retval = -ENODEV;
-		goto done;
-	}
-
-	/* insist the urb is still queued */
-	list_for_each(tmp, &urb->ep->urb_list) {
-		if (tmp == &urb->urb_list)
-			break;
-	}
-	if (tmp != &urb->urb_list) {
-		retval = -EIDRM;
-		goto done;
-	}
 
-	/* Any status except -EINPROGRESS means something already started to
-	 * unlink this URB from the hardware.  So there's no more work to do.
-	 */
-	if (urb->status != -EINPROGRESS) {
-		retval = -EBUSY;
-		goto done;
-	}
+	retval = usb_hcd_check_unlink_urb(hcd, urb, status);
+	if (!retval)
+		retval = unlink1(hcd, urb);
 
-	/* IRQ setup can easily be broken so that USB controllers
-	 * never get completion IRQs ... maybe even the ones we need to
-	 * finish unlinking the initial failed usb_set_address()
-	 * or device descriptor fetch.
-	 */
-	if (!test_bit(HCD_FLAG_SAW_IRQ, &hcd->flags) &&
-			!is_root_hub(urb->dev)) {
-		dev_warn (hcd->self.controller, "Unlink after no-IRQ?  "
-			"Controller is probably using the wrong IRQ.\n");
-		set_bit(HCD_FLAG_SAW_IRQ, &hcd->flags);
-	}
-
-	urb->status = status;
-
-	spin_unlock(&hcd_urb_list_lock);
-	spin_unlock_irqrestore (&urb->lock, flags);
-
-	retval = unlink1 (hcd, urb);
 	if (retval == 0)
 		retval = -EINPROGRESS;
-	return retval;
-
-done:
-	spin_unlock(&hcd_urb_list_lock);
-	spin_unlock_irqrestore (&urb->lock, flags);
-	if (retval != -EIDRM && sys && sys->driver)
-		dev_dbg (sys, "hcd_unlink_urb %p fail %d\n", urb, retval);
+	else if (retval != -EIDRM)
+		dev_dbg(&urb->dev->dev, "hcd_unlink_urb %p fail %d\n",
+				urb, retval);
 	return retval;
 }
 
@@ -1165,7 +1182,8 @@ int usb_hcd_unlink_urb (struct urb *urb, int status)
  */
 void usb_hcd_giveback_urb (struct usb_hcd *hcd, struct urb *urb)
 {
-	urb_unlink(hcd, urb);
+	usb_hcd_unlink_urb_from_ep(hcd, urb);
+	unmap_urb_for_dma(hcd, urb);
 	usbmon_urb_complete (&hcd->self, urb);
 	usb_unanchor_urb(urb);
 
@@ -1194,12 +1212,12 @@ void usb_hcd_endpoint_disable (struct usb_device *udev,
 	struct usb_hcd		*hcd;
 	struct urb		*urb;
 
+	might_sleep();
 	hcd = bus_to_hcd(udev->bus);
-	local_irq_disable ();
 
 	/* ep is already gone from udev->ep_{in,out}[]; no more submits */
 rescan:
-	spin_lock(&hcd_urb_list_lock);
+	spin_lock_irq(&hcd_urb_list_lock);
 	list_for_each_entry (urb, &ep->urb_list, urb_list) {
 		int	tmp;
 		int	is_in;
@@ -1244,13 +1262,11 @@ void usb_hcd_endpoint_disable (struct usb_device *udev,
 		/* list contents may have changed */
 		goto rescan;
 	}
-	spin_unlock(&hcd_urb_list_lock);
-	local_irq_enable ();
+	spin_unlock_irq(&hcd_urb_list_lock);
 
 	/* synchronize with the hardware, so old configuration state
 	 * clears out immediately (and will be freed).
 	 */
-	might_sleep ();
 	if (hcd->driver->endpoint_disable)
 		hcd->driver->endpoint_disable (hcd, ep);