net: zero kobject in rx_queue_release

netif_set_real_num_rx_queues() can decrement and increment
the number of rx queues. For example ixgbe does this as
features and offloads are toggled. Presumably this could
also happen across down/up on most devices if the available
resources changed (cpu offlined).

The kobject needs to be zero'd in this case so that the
state is not preserved across kobject_put()/kobject_init_and_add().

This resolves the following error report.

ixgbe 0000:03:00.0: eth2: NIC Link is Up 10 Gbps, Flow Control: RX/TX
kobject (ffff880324b83210): tried to init an initialized object, something is seriously wrong.
Pid: 1972, comm: lldpad Not tainted 2.6.37-rc18021qaz+ #169
Call Trace:
 [<ffffffff8121c940>] kobject_init+0x3a/0x83
 [<ffffffff8121cf77>] kobject_init_and_add+0x23/0x57
 [<ffffffff8107b800>] ? mark_lock+0x21/0x267
 [<ffffffff813c6d11>] net_rx_queue_update_kobjects+0x63/0xc6
 [<ffffffff813b5e0e>] netif_set_real_num_rx_queues+0x5f/0x78
 [<ffffffffa0261d49>] ixgbe_set_num_queues+0x1c6/0x1ca [ixgbe]
 [<ffffffffa0262509>] ixgbe_init_interrupt_scheme+0x1e/0x79c [ixgbe]
 [<ffffffffa0274596>] ixgbe_dcbnl_set_state+0x167/0x189 [ixgbe]
Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
Acked-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/net-sysfs.c

@@ -712,15 +712,21 @@ static void rx_queue_release(struct kobject *kobj)
 
 
 	map = rcu_dereference_raw(queue->rps_map);
-	if (map)
+	if (map) {
+		RCU_INIT_POINTER(queue->rps_map, NULL);
 		call_rcu(&map->rcu, rps_map_release);
+	}
 
 	flow_table = rcu_dereference_raw(queue->rps_flow_table);
-	if (flow_table)
+	if (flow_table) {
+		RCU_INIT_POINTER(queue->rps_flow_table, NULL);
 		call_rcu(&flow_table->rcu, rps_dev_flow_table_release);
+	}
 
 	if (atomic_dec_and_test(&first->count))
 		kfree(first);
+	else
+		memset(kobj, 0, sizeof(*kobj));
 }
 
 static struct kobj_type rx_queue_ktype = {