dm9000: locking bugfix

This fixes a locking bug in the dm9000 driver.  It calls
request_irq() without setting IRQF_DISABLED ... which is
correct for handlers that support IRQ sharing, since that
behavior is not guaranteed for shared IRQs.  However, its
IRQ handler then wrongly assumes that IRQs are blocked.
So the fix just uses the right spinlock primitives in the
IRQ handler.

NOTE:  this is a classic example of the type of bug which
lockdep currently masks by forcibly setting IRQF_DISABLED
on IRQ handlers that did not request that flag.
Signed-off-by: NDavid Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/dm9000.c

@@ -930,13 +930,15 @@ static irqreturn_t dm9000_interrupt(int irq, void *dev_id)
 	struct net_device *dev = dev_id;
 	board_info_t *db = netdev_priv(dev);
 	int int_status;
+	unsigned long flags;
 	u8 reg_save;
 
 	dm9000_dbg(db, 3, "entering %s\n", __func__);
 
 	/* A real interrupt coming */
 
-	spin_lock(&db->lock);
+	/* holders of db->lock must always block IRQs */
+	spin_lock_irqsave(&db->lock, flags);
 
 	/* Save previous register address */
 	reg_save = readb(db->io_addr);
@@ -972,7 +974,7 @@ static irqreturn_t dm9000_interrupt(int irq, void *dev_id)
 	/* Restore previous register address */
 	writeb(reg_save, db->io_addr);
 
-	spin_unlock(&db->lock);
+	spin_unlock_irqrestore(&db->lock, flags);
 
 	return IRQ_HANDLED;
 }