PROBLEM:        (ZPOB54023)     (Patch ID: OSF375-350405)
********
This is a mandatory patch for SMP systems.

This patch fixes panics that may occur on SMP systems.

The panics occur when one processor is exiting and the other processor
is trying to perform a pmap_tbsync.

The following error message is displayed on the systems:

        "simple_lock: time limit exceeded"

A sample stack trace for the cpu panicking with
"simple_lock: time limit exceeded" is as follows:

   panic("simple_lock: time limit exceeded")
   simple_lock_fault() ["/src/kernel/kern/lock.c":2065]
   simple_lock_time_violation() ["/src/kernel/kern/lock.c":2135]
   psignal_internal() ["/src/kernel/bsd/kern_sig.c":3183]
   psignal_inthread() [/src/kernel/bsd/kern_sig.c":4235]
   exit() ["/src/kernel/bsd/kern_exit.c":1270 ]
   rexit()["/src/kernel/bsd/kern_exit.c":755 ]
   syscall() ["/src/kernel/arch/alpha/syscall_trap.c":540]
   _Xsyscall()[/src/kernel/arch/alpha/locore.s":1209]

A sample stack trace for the cpu performing a pmap_tbsync is as follows:

  cpu_ip_intr() ["/src/kernel/arch/alpha/cpu.c":647]
  _XentInt()["/src/kernel/arch/alpha/locore.s":1076]
  mb()["/src/kernel/arch/alpha/pal_lib.s":252]
  xcpu_puts_ipir() ["/src/kernel/bsd/subr_prf.c":866]
  event_timeout()["/src/kernel/arch/alpha/cpu.c":1003]
  pmap_update_send()["/src/kernel/arch/alpha/pmap_update.c":250]
  pmap_tbsync()["/src/kernel/arch/alpha/pmap.c":4151]
  pmap_remove_range()["/src/kernel/arch/alpha/pmap.c":2175]
  pmap_remove()["/src/kernel/arch/alpha/pmap.c":2310]
  pmap_protect()["/src/kernel/arch/alpha/pmap.c":2374]
  free()["/src/kernel/bsd/kern_malloc.c":1129]
  m_free()["/src/kernel/bsd/uipc_mbuf.c":520"]
  m_freem()["/src/kernel/bsd/uipc_mbuf.c":529"]
  xnaread()["/src/kernel/io/dec/netif/if_xna.c":1372"]
  _XentInt()["/src/kernel/arch/alpha/locore.s":1049]
  issig() ["/src/kernel/bsd/kern_sig.c":4678]
  mpsleep()["/src/kernel/bsd/kern_synch.c":581]
  sigsuspend() ["/src/kernel/bsd/kern_sig.c":2228]
  syscall()["/src/kernel/arch/alpha/syscall_trap.c":540"]
  _Xsyscall()["/src/kernel/arch/alpha/locore.s":1209]