Real-Time Preemption, -RT-2.6.9-rc4-mm1-U6

i have released the -U6 Real-Time Preemption patch:
 
  http://redhat.com/~mingo/realtime-preempt/realtime-preemp...

this is a fixes-only release.

found and fixed the 'big bug' that was probably the one causing
stability problems for a number of people. There was a small window for
a task double-free race to occur, causing all sorts of crashes later on.
This bug could trigger on UP and SMP systems alike, on SMP being a bit
more frequent.

Also, a common networking deadlock was found and fixed as well, using
the deadlock detector.

Changes since -U5:

- crash bug: fix task double free caused by irq-preemption of 
  do_exit(). This got introduced in -U5 as part of a simplification of
  the zombie-reaping rewrite that the -U series did. That rewrite had an 
  unrobustness which got triggered by -U5 in a subtle way, opening up a
  small window at the end of do_exit() for an interrupt-triggered
  preemption to cause a double-free. This could fix some of the crashes
  reported by Rui Nuno Capela, Mark H Johnson.

- deadlock bug: fix networking deadlock reported by Matthew L Foster.
  Restructured the way the RT-RCU locking of ptype_lock is done - it's
  cleaner and more obvious now (besides being correct). This could also
  fix the deadlock reported by Michal Schmidt.

- deadlock bug: fix NFS startup breakage related to semaphore abuse,
  patch from Thomas Gleixner.

- build bug: fix aha152x.c, based on patch from K.R. Foley.

- build bug: fix compilation error in qla2xxx. (reported by Fernando
  Pablo Lopez-Lezcano and Mark H Johnson)

- build bug: fix !PREEMPT_REALTIME compilation error. (reported by
  Matthew L Foster)

- build bug: fix ipmi-watchdog compilation error. (reported by Mark H 
  Johnson)

- tracer fix: if an assert happens within the tracer then we'd get into
  infinite recursion. The fix was to correctly nest tracing on/off
  points.

- debug enhancement: added a few more asserts to catch underflowing 
  atomic counters. (this made the task double-free trigger earlier.)

- debug enhancement: extended CONFIG_DEBUG_STACKOVERFLOW to be 
  mcount()-driven as well. This helps in catching stack overflows much
  more reliably than the do_IRQ() based method.

to create a -U6 tree from scratch, the patching order is:

   http://kernel.org/pub/linux/kernel/v2.6/linux-2.6.8.tar.bz2
 + http://kernel.org/pub/linux/kernel/v2.6/testing/patch-2.6...
 + http://kernel.org/pub/linux/kernel/people/akpm/patches/2....
 + http://redhat.com/~mingo/realtime-preempt/realtime-preemp...

	Ingo
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