atl1c: Fix work event interrupt/task races

The mechanism used to initiate work events from the interrupt
handler has a classic read/modify/write race between the interrupt
handler that sets the condition, and the worker task that reads and
clears the condition. Close these races by using atomic
bit fields.

Cc: stable@kernel.org
Cc: Jie Yang <jie.yang@atheros.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/atl1c/atl1c.h

@@ -566,9 +566,9 @@ struct atl1c_adapter {
 #define __AT_TESTING        0x0001
 #define __AT_RESETTING      0x0002
 #define __AT_DOWN           0x0003
-	u8 work_event;
-#define ATL1C_WORK_EVENT_RESET 		0x01
-#define ATL1C_WORK_EVENT_LINK_CHANGE	0x02
+	unsigned long work_event;
+#define	ATL1C_WORK_EVENT_RESET		0
+#define	ATL1C_WORK_EVENT_LINK_CHANGE	1
 	u32 msg_enable;
 
 	bool have_msi;

drivers/net/atl1c/atl1c_main.c

@@ -325,7 +325,7 @@ static void atl1c_link_chg_event(struct atl1c_adapter *adapter)
 		}
 	}
 
-	adapter->work_event |= ATL1C_WORK_EVENT_LINK_CHANGE;
+	set_bit(ATL1C_WORK_EVENT_LINK_CHANGE, &adapter->work_event);
 	schedule_work(&adapter->common_task);
 }
 
@@ -337,20 +337,16 @@ static void atl1c_common_task(struct work_struct *work)
 	adapter = container_of(work, struct atl1c_adapter, common_task);
 	netdev = adapter->netdev;
 
-	if (adapter->work_event & ATL1C_WORK_EVENT_RESET) {
-		adapter->work_event &= ~ATL1C_WORK_EVENT_RESET;
+	if (test_and_clear_bit(ATL1C_WORK_EVENT_RESET, &adapter->work_event)) {
 		netif_device_detach(netdev);
 		atl1c_down(adapter);
 		atl1c_up(adapter);
 		netif_device_attach(netdev);
-		return;
 	}
 
-	if (adapter->work_event & ATL1C_WORK_EVENT_LINK_CHANGE) {
-		adapter->work_event &= ~ATL1C_WORK_EVENT_LINK_CHANGE;
+	if (test_and_clear_bit(ATL1C_WORK_EVENT_LINK_CHANGE,
+		&adapter->work_event))
 		atl1c_check_link_status(adapter);
-	}
-	return;
 }
 
 
@@ -369,7 +365,7 @@ static void atl1c_tx_timeout(struct net_device *netdev)
 	struct atl1c_adapter *adapter = netdev_priv(netdev);
 
 	/* Do the reset outside of interrupt context */
-	adapter->work_event |= ATL1C_WORK_EVENT_RESET;
+	set_bit(ATL1C_WORK_EVENT_RESET, &adapter->work_event);
 	schedule_work(&adapter->common_task);
 }