mb_read

- alpha: used for MUTEX_RECEIVE, defined as mb instruction
- arm: drain_writebuf
- hppa: __sync (i.e., sync instruction)
- ia64: mf instruction
- m68k: used for MUTEX_RECEIVE, defined as insn barrier
- mips:
  . _HARDKERNEL: __insn_barrier on MIPS1, sync instruction otherwise
  . !_HARDKERNEL: alias for membar_sync
- powerpc: used for MUTEX_RECEIVE, defined as isync instruction
- sh3: insn barrier
- sparc:
  . v9: membar #LoadLoad
  . <v9: a single store instruction
- sparc64: used for MUTEX_RECEIVE and RW_RECEIVE, defined as on sparc
- vax: empty

mb_write

- alpha: mb instruction
- arm: drain_writebuf
- hppa: used in MUTEX_SET_WAITERS, defined as __sync (i.e., sync instruction)
- ia64: mf instruction
- m68k: insn barrier
- mips: used in __cpu_simple_unlock
  . _HARDKERNEL: __insn_barrier on MIPS1, sync instruction otherwise
  . !_HARDKERNEL: alias for membar_producer on Octeon,
                  alias for membar_sync otherwise
- powerpc: sync instruction
- sh3: insn barrier
- sparc: insn barrier
- vax: empty

mb_memory

- alpha: mb instruction
- arm: drain_writebuf
- hppa: used in MUTEX_SET_WAITERS, defined as __sync (i.e., sync instruction)
- ia64: mf instruction
- m68k: used in MUTEX_GIVE, defined as insn barrier
- mips: used in __cpu_simple_lock_init and __cpu_simple_unlock
  . _HARDKERNEL: __insn_barrier on MIPS1, sync instruction otherwise
  . !_HARDKERNEL: alias for membar_sync
- powerpc: used in MUTEX_GIVE, defined as sync instruction
- sh3: insn barrier
- sparc:
  . v9: membar #MemIssue
  . <v9: a single store instruction