bonding: fix state transition issue in link monitoring

Since de77ecd4ef02 ("bonding: improve link-status update in mii-monitoring"), the bonding driver has utilized two separate variables to indicate the next link state a particular slave should transition to. Each is used to communicate to a different portion of the link state change commit logic; one to the bond_miimon_commit function itself, and another to the state transition logic. Unfortunately, the two variables can become unsynchronized, resulting in incorrect link state transitions within bonding. This can cause slaves to become stuck in an incorrect link state until a subsequent carrier state transition. The issue occurs when a special case in bond_slave_netdev_event sets slave->link directly to BOND_LINK_FAIL. On the next pass through bond_miimon_inspect after the slave goes carrier up, the BOND_LINK_FAIL case will set the proposed next state (link_new_state) to BOND_LINK_UP, but the new_link to BOND_LINK_DOWN. The setting of the final link state from new_link comes after that from link_new_state, and so the slave will end up incorrectly in _DOWN state. Resolve this by combining the two variables into one.

JVJay Vosburgh committed 7 years ago