Deadlock Avoidance in FreeBSD SMPng

• Hard lock order

  • Applies to most mutexes and sx locks
  • Disallow lock cycles
  • WITNESS lock verification tool

• Variable hierarchal lock order

  • Lock order a property of data structures
  • At any given moment, the lock order is defined
  • However, it may change as data structure changes

• Master locks

  • Master lock used to serialize simultaenous access to multiple leaf locks