uio: fix a sleep-in-atomic-context bug in uio_dmem_genirq_irqcontrol()

The driver may sleep while holding a spinlock.
The function call path (from bottom to top) in Linux 4.19 is:

kernel/irq/manage.c, 523:
	synchronize_irq in disable_irq
drivers/uio/uio_dmem_genirq.c, 140:
	disable_irq in uio_dmem_genirq_irqcontrol
drivers/uio/uio_dmem_genirq.c, 134:
	_raw_spin_lock_irqsave in uio_dmem_genirq_irqcontrol

synchronize_irq() can sleep at runtime.

To fix this bug, disable_irq() is called without holding the spinlock.

This bug is found by a static analysis tool STCheck written by myself.

Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
Link: https://lore.kernel.org/r/20191218094405.6009-1-baijiaju1990@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/uio/uio_dmem_genirq.c

@@ -132,11 +132,13 @@ static int uio_dmem_genirq_irqcontrol(struct uio_info *dev_info, s32 irq_on)
 	if (irq_on) {
 		if (test_and_clear_bit(0, &priv->flags))
 			enable_irq(dev_info->irq);
+		spin_unlock_irqrestore(&priv->lock, flags);
 	} else {
-		if (!test_and_set_bit(0, &priv->flags))
+		if (!test_and_set_bit(0, &priv->flags)) {
+			spin_unlock_irqrestore(&priv->lock, flags);
 			disable_irq(dev_info->irq);
+		}
 	}
-	spin_unlock_irqrestore(&priv->lock, flags);
 
 	return 0;
 }