drivers: usb: core: Minimize irq disabling in usb_sg_cancel()

Restructure usb_sg_cancel() so we don't have to disable interrupts
while cancelling the URBs.
Suggested-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: David Mosberger <davidm@egauge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/core/message.c

@@ -577,18 +577,18 @@ EXPORT_SYMBOL_GPL(usb_sg_wait);
 void usb_sg_cancel(struct usb_sg_request *io)
 {
 	unsigned long flags;
+	int i, retval;
 
 	spin_lock_irqsave(&io->lock, flags);
-
-	/* shut everything down, if it didn't already */
-	if (!io->status) {
-		int i;
-
+	if (io->status) {
+		spin_unlock_irqrestore(&io->lock, flags);
+		return;
+	}
+	/* shut everything down */
 	io->status = -ECONNRESET;
-		spin_unlock(&io->lock);
-		for (i = 0; i < io->entries; i++) {
-			int retval;
+	spin_unlock_irqrestore(&io->lock, flags);
 
+	for (i = io->entries - 1; i >= 0; --i) {
 		usb_block_urb(io->urbs[i]);
 
 		retval = usb_unlink_urb(io->urbs[i]);
@@ -599,9 +599,6 @@ void usb_sg_cancel(struct usb_sg_request *io)
 			dev_warn(&io->dev->dev, "%s, unlink --> %d\n",
 				 __func__, retval);
 	}
-		spin_lock(&io->lock);
-	}
-	spin_unlock_irqrestore(&io->lock, flags);
 }
 EXPORT_SYMBOL_GPL(usb_sg_cancel);