RFC Preview of RCU changes for 3.3

Hello!

This patchset permits idle tasks to use RCU read-side critical sections, although they are still prohibited between tick_nohz_idle_exit_norcu() and tick_nohz_idle_exit_norcu(); makes synchronize_sched_expedited() better able to share work among concurrent callers, allows ftrace_dump() to be invoked from modules, dumps tracing upon detection of an rcutorture failure, detects illegal use of RCU read-side critical sections from extended quiescent states, legitimizes the pre-existin use of RCU in the idle notifiers, fixes a memory-barrier botch, introduces an SRCU-like bulk reference count, improve dynticks entry/exit tracing, further improves RCU's ability to allow a given CPU to enter dyntick-idle mode quickly, fixes idle-task checks, updates documentation, and additional fixes from a still-ongoing top-to-bottom inspection of RCU. The patches are as follows:

1. Strengthen memory barriers used in PowerPC value-returning
atomics and locking primitives. It is likely that this commit will be superseded by something from the powerpc maintainers. The need for this strengthening was validated by tooling from Peter Sewell's group at the University of Cambridge.
2. Rename ->signaled to ->fqs_state to clarify the code.
3. Fix a race that could permit RCU-preempt expedited grace
periods to complete too soon.
4. Improve synchronize_sched_expedited()'s ability to share work
among concurrent callers.
5. Document the troubleshooting of lockdep lock-class leaks.
6. Explicitly track idleness, which is a step towards permitting
the idle tasks to contain RCU read-side critical sections (but only outside the body of the idle loop).
7,8. Add an EXPORT_SYMBOL_GPL() for ftrace_dump() so that
rcutorture can dump the trace buffer upon detection of an error, and then make rcutorture do the dumping.
9. Document a failing scheduling-clock tick as yet another
possible cause of RCU CPU stall warnings.
10. Disable preemption in rcu_is_cpu_idle() in order to prevent
spurious lockdep-RCU splats.
11. Remove a useless self-awaken when setting up expedited grace
periods, courtesy of Thomas Gleixner and the -rt effort.
12-17. Make lockdep-RCU warn when RCU read-side primitives are
invoked from an idle RCU extended quiescent state, mostly courtesy of Frederic Weisbecker.
18-23. Separate out the scheduler-clock tick's idea of dyntick
idle from RCU's notion of an idle extended quiescent state, mostly courtesy of Frederic Weisbecker. These commits are needed for Frederic's work to suppress the scheduler-clock tick when there is but one runnable task on a given CPU.
24. Introduce a bulk reference count, which is related to SRCU,
but which allows a reference to be acquired in an irq handler and released by the task that was interrupted.
25-26. Improve dyntick-idle tracing and diagnostics.
27. Allow CPUs with pending RCU callbacks to enter dyntick-idle
mode. Beware this commit, as it compiled and passed rcutorture on the first try, which historically has indicated the presence of subtle and highly destructive bugs.
28. Fix RCU's determination of whether or not it is running in the
context of an idle task.

For a testing-only version of this patchset from git, please see the following subject-to-rebase branch:

git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git rcu/dev

Thanx, Paul

------------------------------------------------------------------------

 arch/arm/kernel/process.c                  |    4 
 arch/avr32/kernel/process.c                |    4 
 arch/blackfin/kernel/process.c             |    4 
 arch/microblaze/kernel/process.c           |    4 
 arch/mips/kernel/process.c                 |    4 
 arch/openrisc/kernel/idle.c                |    4 
 arch/powerpc/kernel/idle.c                 |   20 +
 arch/powerpc/platforms/iseries/setup.c     |    8 
 arch/s390/kernel/process.c                 |    4 
 arch/sh/kernel/idle.c                      |    4 
 arch/sparc/kernel/process_64.c             |    4 
 arch/tile/kernel/process.c                 |    4 
 arch/um/kernel/process.c                   |    4 
 arch/unicore32/kernel/process.c            |    4 
 arch/x86/kernel/process_32.c               |    4 
 arch/x86/kernel/process_64.c               |   14 -
 b/Documentation/RCU/stallwarn.txt          |    5 
 b/Documentation/RCU/trace.txt              |    4 
 b/Documentation/lockdep-design.txt         |   61 +++++
 b/arch/arm/kernel/process.c                |    4 
 b/arch/avr32/kernel/process.c              |    4 
 b/arch/blackfin/kernel/process.c           |    4 
 b/arch/microblaze/kernel/process.c         |    4 
 b/arch/mips/kernel/process.c               |    4 
 b/arch/openrisc/kernel/idle.c              |    4 
 b/arch/powerpc/include/asm/synch.h         |    6 
 b/arch/powerpc/kernel/idle.c               |    4 
 b/arch/powerpc/platforms/iseries/setup.c   |    8 
 b/arch/powerpc/platforms/pseries/lpar.c    |    4 
 b/arch/s390/kernel/process.c               |    4 
 b/arch/sh/kernel/idle.c                    |    4 
 b/arch/sparc/kernel/process_64.c           |    4 
 b/arch/tile/kernel/process.c               |    4 
 b/arch/um/kernel/process.c                 |    4 
 b/arch/unicore32/kernel/process.c          |    4 
 b/arch/x86/kernel/apic/apic.c              |    6 
 b/arch/x86/kernel/apic/io_apic.c           |    2 
 b/arch/x86/kernel/cpu/mcheck/therm_throt.c |    2 
 b/arch/x86/kernel/cpu/mcheck/threshold.c   |    2 
 b/arch/x86/kernel/irq.c                    |    6 
 b/arch/x86/kernel/process_32.c             |    4 
 b/arch/x86/kernel/process_64.c             |    4 
 b/include/linux/hardirq.h                  |   21 --
 b/include/linux/rcupdate.h                 |   21 --
 b/include/linux/srcu.h                     |   36 ++-
 b/include/linux/tick.h                     |   11 -
 b/include/trace/events/rcu.h               |   10 
 b/kernel/lockdep.c                         |   22 ++
 b/kernel/rcu.h                             |    7 
 b/kernel/rcupdate.c                        |   10 
 b/kernel/rcutiny.c                         |  124 ++++++++++--
 b/kernel/rcutorture.c                      |   18 +
 b/kernel/rcutree.c                         |   16 -
 b/kernel/rcutree.h                         |    4 
 b/kernel/rcutree_plugin.h                  |    7 
 b/kernel/rcutree_trace.c                   |    2 
 b/kernel/softirq.c                         |    2 
 b/kernel/srcu.c                            |    3 
 b/kernel/time/tick-sched.c                 |    6 
 b/kernel/trace/trace.c                     |    1 
 include/linux/rcupdate.h                   |  139 ++++++++-----
 include/linux/srcu.h                       |   55 +++++
 include/linux/tick.h                       |   59 ++++-
 include/trace/events/rcu.h                 |   41 +++
 kernel/rcupdate.c                          |    2 
 kernel/rcutiny.c                           |   45 ++--
 kernel/rcutree.c                           |  298 ++++++++++++++++++++---------
 kernel/rcutree.h                           |   22 --
 kernel/rcutree_plugin.h                    |  175 +++++++++++++----
 kernel/rcutree_trace.c                     |   10 
 kernel/softirq.c                           |    2 
 kernel/time/tick-sched.c                   |  118 ++++++-----
 72 files changed, 1080 insertions(+), 467 deletions(-)