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Subject[patch] Real-Time Preemption, -RT-2.6.9-rc4-mm1-U6

i have released the -U6 Real-Time Preemption patch:

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

- 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

- 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:

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