cvs commit: src/sys/kern kern_condvar.c kern_lock.c kern_sig.c kern_sx.c kern_synch.c kern_thread.c subr_sleepqueue.c src/sys/sys proc.h sleepqueue.h src/sys/vm vm_glue.c

John Baldwin jhb at
Tue Aug 5 20:03:41 UTC 2008

jhb         2008-08-05 20:02:31 UTC

  FreeBSD src repository

  Modified files:
    sys/kern             kern_condvar.c kern_lock.c kern_sig.c 
                         kern_sx.c kern_synch.c kern_thread.c 
    sys/sys              proc.h sleepqueue.h 
    sys/vm               vm_glue.c 
  SVN rev 181334 on 2008-08-05 20:02:31Z by jhb
  If a thread that is swapped out is made runnable, then the setrunnable()
  routine wakes up proc0 so that proc0 can swap the thread back in.
  Historically, this has been done by waking up proc0 directly from
  setrunnable() itself via a wakeup().  When waking up a sleeping thread
  that was swapped out (the usual case when waking proc0 since only sleeping
  threads are eligible to be swapped out), this resulted in a bit of
  recursion (e.g. wakeup() -> setrunnable() -> wakeup()).
  With sleep queues having separate locks in 6.x and later, this caused a
  spin lock LOR (sleepq lock -> sched_lock/thread lock -> sleepq lock).
  An attempt was made to fix this in 7.0 by making the proc0 wakeup use
  the ithread mechanism for doing the wakeup.  However, this required
  grabbing proc0's thread lock to perform the wakeup.  If proc0 was asleep
  elsewhere in the kernel (e.g. waiting for disk I/O), then this degenerated
  into the same LOR since the thread lock would be some other sleepq lock.
  Fix this by deferring the wakeup of the swapper until after the sleepq
  lock held by the upper layer has been locked.  The setrunnable() routine
  now returns a boolean value to indicate whether or not proc0 needs to be
  woken up.  The end result is that consumers of the sleepq API such as
  *sleep/wakeup, condition variables, sx locks, and lockmgr, have to wakeup
  proc0 if they get a non-zero return value from sleepq_abort(),
  sleepq_broadcast(), or sleepq_signal().
  Discussed with: jeff
  Glanced at by:  sam
  Tested by:      Jurgen Weber  jurgen - ish com au
  MFC after:      2 weeks
  Revision  Changes    Path
  1.64      +11 -2     src/sys/kern/kern_condvar.c
  1.135     +16 -9     src/sys/kern/kern_lock.c
  1.362     +10 -2     src/sys/kern/kern_sig.c
  1.61      +17 -6     src/sys/kern/kern_sx.c
  1.312     +17 -15    src/sys/kern/kern_synch.c
  1.275     +11 -3     src/sys/kern/kern_thread.c
  1.56      +49 -18    src/sys/kern/subr_sleepqueue.c
  1.517     +1 -1      src/sys/sys/proc.h
  1.15      +3 -3      src/sys/sys/sleepqueue.h
  1.232     +14 -37    src/sys/vm/vm_glue.c

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