usb: usb-skeleton: use irqsave() in USB's complete callback

The USB completion callback does not disable interrupts while acquiring
the lock. We want to remove the local_irq_disable() invocation from
__usb_hcd_giveback_urb() and therefore it is required for the callback
handler to disable the interrupts while acquiring the lock.
The callback may be invoked either in IRQ or BH context depending on the
USB host controller.
Use the _irqsave() variant of the locking primitives.
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/usb-skeleton.c

@@ -159,10 +159,11 @@ static int skel_flush(struct file *file, fl_owner_t id)
 static void skel_read_bulk_callback(struct urb *urb)
 {
 	struct usb_skel *dev;
+	unsigned long flags;
 
 	dev = urb->context;
 
-	spin_lock(&dev->err_lock);
+	spin_lock_irqsave(&dev->err_lock, flags);
 	/* sync/async unlink faults aren't errors */
 	if (urb->status) {
 		if (!(urb->status == -ENOENT ||
@@ -177,7 +178,7 @@ static void skel_read_bulk_callback(struct urb *urb)
 		dev->bulk_in_filled = urb->actual_length;
 	}
 	dev->ongoing_read = 0;
-	spin_unlock(&dev->err_lock);
+	spin_unlock_irqrestore(&dev->err_lock, flags);
 
 	wake_up_interruptible(&dev->bulk_in_wait);
 }
@@ -331,6 +332,7 @@ static ssize_t skel_read(struct file *file, char *buffer, size_t count,
 static void skel_write_bulk_callback(struct urb *urb)
 {
 	struct usb_skel *dev;
+	unsigned long flags;
 
 	dev = urb->context;
 
@@ -343,9 +345,9 @@ static void skel_write_bulk_callback(struct urb *urb)
 				"%s - nonzero write bulk status received: %d\n",
 				__func__, urb->status);
 
-		spin_lock(&dev->err_lock);
+		spin_lock_irqsave(&dev->err_lock, flags);
 		dev->errors = urb->status;
-		spin_unlock(&dev->err_lock);
+		spin_unlock_irqrestore(&dev->err_lock, flags);
 	}
 
 	/* free up our allocated buffer */