cvs commit: src/sys/i386/i386 vm_machdep.c src/sys/kern kern_exit.c lwkt_thread.c src/sys/sys thread.h

[Matthew Dillon <dillon@xxxxxxxxxxxxxxxxxxxxxxx>]

dillon      2005/12/02 14:02:20 PST

DragonFly src repository

  Modified files:
    sys/i386/i386        vm_machdep.c 
    sys/kern             kern_exit.c lwkt_thread.c 
    sys/sys              thread.h 
  Log:
  Fix a process exit/wait race.  The wait*() code was making a faulty test
  to determine that the exiting process had completely exited and was no
  longer running.  Testing the TDF_RUNNING flag is insufficient because an
  exiting process may block at various points after becoming a Zombie, but
  before it deschedules itself for the last time.
  
  Add a new flag, TDF_EXITING, which is set just prior to a thread descheduling
  itself for the last time.  The reaper then checks that TDF_EXITING is set
  and TDF_RUNNING is clear.
  
  Fix a second faulty test in both the exit and the thread cpu migration
  code.  If a thread gets preempted, TDF_RUNNING will be temporarily cleared,
  so testing TDF_RUNNING is not sufficient by itself.  We must also test
  the TDF_PREEMPT_LOCK flag to be sure that it is also clear.
  
  So the grand result is that to really be sure the zombie process has been
  completely descheduled and is no longer running or will ever run again,
  the TDF_EXITING, TDF_RUNNING, *and* TDF_PREEMPT_LOCK flags must be tested
  and all must be clear except for TDF_EXITING.
  
  It should be noted that TDF_RUNNING on the previously scheduled process
  is always cleared AFTER we have context-switched into the next scheduled
  thread or the idle thread, so seeing a cleared TDF_RUNNING along with the
  appropriate state for the other flags does in fact guarentee that the thread
  in question is no longer using its stack in any way.
  
  Reported-by: Stefan Krueger <skrueger@xxxxxxxxxxxxxxxx>
  
  Revision  Changes    Path
  1.39      +1 -0      src/sys/i386/i386/vm_machdep.c
  1.51      +23 -15    src/sys/kern/kern_exit.c
  1.89      +2 -2      src/sys/kern/lwkt_thread.c
  1.76      +4 -1      src/sys/sys/thread.h


http://www.dragonflybsd.org/cvsweb/src/sys/i386/i386/vm_machdep.c.diff?r1=1.38&r2=1.39&f=u
http://www.dragonflybsd.org/cvsweb/src/sys/kern/kern_exit.c.diff?r1=1.50&r2=1.51&f=u
http://www.dragonflybsd.org/cvsweb/src/sys/kern/lwkt_thread.c.diff?r1=1.88&r2=1.89&f=u
http://www.dragonflybsd.org/cvsweb/src/sys/sys/thread.h.diff?r1=1.75&r2=1.76&f=u