bonding 802.3ad: Fix the state machine locking v2

Changes since v1:
* Clarify an unclear comment
* Move a (possible) name change to a separate patch

The ad_rx_machine, ad_periodic_machine and ad_port_selection_logic
functions all inspect and alter common fields within the port structure.
Previous to this patch, only the ad_rx_machines were mutexed, and the
periodic and port_selection could run unmutexed against an ad_rx_machine
trigged by an arriving LACPDU.

This patch remedies the situation by protecting all the state machines
from concurrency. This is accomplished by locking around all the state
machines for a given port, which are executed at regular intervals; and
the ad_rx_machine when handling an incoming LACPDU.
Signed-off-by: Nils Carlson <nils.carlson@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/bonding/bond_3ad.c

@@ -1025,9 +1025,6 @@ static void ad_rx_machine(struct lacpdu *lacpdu, struct port *port)
 {
 	rx_states_t last_state;
 
-	// Lock to prevent 2 instances of this function to run simultaneously(rx interrupt and periodic machine callback)
-	__get_rx_machine_lock(port);
-
 	// keep current State Machine state to compare later if it was changed
 	last_state = port->sm_rx_state;
 
@@ -1133,7 +1130,6 @@ static void ad_rx_machine(struct lacpdu *lacpdu, struct port *port)
 				pr_err("%s: An illegal loopback occurred on adapter (%s).\n"
 				       "Check the configuration to verify that all adapters are connected to 802.3ad compliant switch ports\n",
 				       port->slave->dev->master->name, port->slave->dev->name);
-				__release_rx_machine_lock(port);
 				return;
 			}
 			__update_selected(lacpdu, port);
@@ -1153,7 +1149,6 @@ static void ad_rx_machine(struct lacpdu *lacpdu, struct port *port)
 			break;
 		}
 	}
-	__release_rx_machine_lock(port);
 }
 
 /**
@@ -2155,6 +2150,12 @@ void bond_3ad_state_machine_handler(struct work_struct *work)
 			goto re_arm;
 		}
 
+		/* Lock around state machines to protect data accessed
+		 * by all (e.g., port->sm_vars).  ad_rx_machine may run
+		 * concurrently due to incoming LACPDU.
+		 */
+		__get_rx_machine_lock(port);
+
 		ad_rx_machine(NULL, port);
 		ad_periodic_machine(port);
 		ad_port_selection_logic(port);
@@ -2164,6 +2165,8 @@ void bond_3ad_state_machine_handler(struct work_struct *work)
 		// turn off the BEGIN bit, since we already handled it
 		if (port->sm_vars & AD_PORT_BEGIN)
 			port->sm_vars &= ~AD_PORT_BEGIN;
+
+		__release_rx_machine_lock(port);
 	}
 
 re_arm:
@@ -2200,7 +2203,10 @@ static void bond_3ad_rx_indication(struct lacpdu *lacpdu, struct slave *slave, u
 		case AD_TYPE_LACPDU:
 			pr_debug("Received LACPDU on port %d\n",
 				 port->actor_port_number);
+			/* Protect against concurrent state machines */
+			__get_rx_machine_lock(port);
 			ad_rx_machine(lacpdu, port);
+			__release_rx_machine_lock(port);
 			break;
 
 		case AD_TYPE_MARKER: