RFC v2 RCU cleanups and simplified preemptable RCU

[Not yet for inclusion, but making good progress.]

This patchset contains some RCU cleanups as follows:

o Move private definitions from include/linux/rcutree.h to
kernel/rcutree.h

o Rename variables and functions so that RCU-sched is an
underlying definition, along with RCU-bh and (when so configured) RCU-preempt. RCU then maps to either RCU-sched or RCU-preempt, depending on configuration.

o Consolidate sparse and lockdep into include/linux/rcupdate.h
so that all RCU implementations are set up properly.

With these in place, we add configurable preemptable-RCU functionality to kernel/rcutree.c. This new implementation has much faster and simpler read-side primitives (roughly that of Classic RCU built with CONFIG_PREEMPT), and has update-side performance equal to Classic RCU (at least in absence of blocking/preemption of read-side critical sections). This new implementation should eventually replace the old preemptable RCU, which would remove 2099 lines of code from the kernel, for a net removal of more than 1000 lines of code.

This patchset is undoubtably buggy, and does not have RCU priority boosting, though it does have the necessary tracking of tasks blocked in RCU read-side critical sections.

Changes from v1 (http://lkml.org/lkml/2009/7/23/294):

o Fixes some locking problems detected by lockdep.

o Disable irqs in quiescent-state-detection code, and fix handling
of scheduling-clock interrupt always occurring in RCU read-side critical section.

o Fix sparse annotations.

o Apply feedback from Mathieu Desnoyers.

o Fix x86 kernel-build errors.

o Now passes moderate (multi-hour) rcutorture tests.

Shortcomings:

o Only moderately tested, probably still quite buggy. CPU hotplug
not yet tested heavily, for example.

o Probably does not even compile for all of the relevant
combinations of kernel configuration variables.

o Lacks RCU priority boosting.

 b/Documentation/RCU/trace.txt |    7 
 b/include/linux/init_task.h   |   15 +
 b/include/linux/rcupdate.h    |   21 +-
 b/include/linux/rcupreempt.h  |    4 
 b/include/linux/rcutree.h     |  211 --------------------
 b/include/linux/sched.h       |   37 +++
 b/init/Kconfig                |   22 +-
 b/kernel/Makefile             |    1 
 b/kernel/exit.c               |    1 
 b/kernel/fork.c               |    5 
 b/kernel/rcupreempt.c         |    8 
 b/kernel/rcutree.c            |    2 
 b/kernel/rcutree.h            |  238 +++++++++++++++++++++++
 b/kernel/rcutree_plugin.h     |  428 ++++++++++++++++++++++++++++++++++++++++++
 b/kernel/rcutree_trace.c      |    2 
 b/kernel/sched.c              |    2 
 b/kernel/softirq.c            |    5 
 include/linux/rcupdate.h      |   48 ++++
 include/linux/rcupreempt.h    |    8 
 include/linux/rcutree.h       |   43 ++--
 kernel/rcutree.c              |  207 +++++++++++++-------
 kernel/rcutree.h              |   13 +
 kernel/rcutree_trace.c        |   40 ++-
 23 files changed, 1018 insertions(+), 350 deletions(-)