[patch] Real-Time Preemption, -RT-2.6.9-rc4-mm1-U5

[Ingo Molnar <mingo@elte.hu>]

i have released the -U5 Real-Time Preemption patch:

  http://redhat.com/~mingo/voluntary-preempt/voluntary-preempt-2.6.9-rc4-mm1-U5

this is a release intended to increase stability, but since it also
includes new debug features and related cleanups it might introduce new
regressions. Be careful.

there are two big changes:

 - debug feature: automatic semaphore/rwsem deadlock detection, based on
   the code from Igor Manyilov and Bill Huey.

this is a very nice feature that should help in debugging the remaining
deadlocks. The deadlock detection feature has already helped me fix a
bug that was causing hangs in the VFS, so it's really useful.

 - generic semaphore implementation

the generic semaphore implementation (which uses rwsems) makes it
possible to use the deadlock detection mechanism for all the mutex types
we currently have: semaphores, rw-semaphores, spinlock-mutexes and
rwlock-mutexes. Another benefit is that PREEMPT_REALTIME becomes much
more portable this way. (although it's still x86-only at the moment.)

other changes since -U4:

 - crash fix: fixed a possible "unbound recursion upon IRQ entry" bug.
   introduced preempt_schedule_irq() which now schedules without
   enabling interrupts again, preventing new IRQs from hitting this
   task again and triggering preemption. This might fix the
   'infinite stackdumps' problem Rui Nuno Capela was seeing.

 - deadlock fix: is_subdir()'s PREEMPT_REALTIME locking was buggy. This 
   could perhaps fix the other problem reported by Rui Nuno Capela.

 - i8253_lock fixes: apm, hd.c, gameport.c and analog.c were all 
   improperly importing the variable while overriding the prototype. 
   This fixes the bug reported by Florian Schmidt.

 - possible crash fix: one particular lock in selinux has to be 
   mutex-based, because while held it calls other mutex-using code.

 - two more selinux locks converted to raw spinlocks, because they were
   called from within raw-critical sections.

 - debug feature: enforce interrupts-enabled upon schedule().
   (Note that this does not break sleep_on() because sleep_on() does not
   disable interrupts in the PREEMPT_REALTIME mode. It might break with 
   !PREEMPT_REALTIME though.)

 - locking cleanup: converted the IPC code from raw spinlocks & RCU to
   spinlock-mutexes.

 - code cleanup: cleaned up the generic rwsem code.

 - debug feature: implemented /proc/sys/kernel/trace_verbose runtime
   flag (default:0), which enables a much more verbose printout in
   /proc/latency_trace.  This trace format can be useful in e.g. 
   debugging timestamp weirdnesses.

 - irqs-off fix: there was one codepath where irqd would call schedule() 
   with interrupts disabled.

 - debug feature: the NMI entries in the latency trace now also include 
   the last-observed-EFLAGS value. Can be useful in figuring out what a
   certain CPU is doing and why.

 - cleanup: fixed preemption-off ordering: often the spinlock (and 
   scheduler) code would re-enable preemption and interrupts in the
   wrong order, opening up a small window for an interrupt handler to
   fit in and increase the latency of that almost-finished critical
   section.

 - cleanup: consolidated various bug-printouts. It should now be easy to
   find whether anything bad happens even amongst lots of preempt-timing
   printouts: 'dmesg | grep BUG'.

to create a -U5 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-2.6.9-rc4.bz2
 + http://kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.9-rc4/2.6.9-rc4-mm1/2.6.9-rc4-mm1.bz2
 + http://redhat.com/~mingo/voluntary-preempt/voluntary-preempt-2.6.9-rc4-mm1-U5

	Ingo