Miscellaneous fixes for 3.20

Hello!

This series contains miscellaneous fixes for 3.20:

1. Make rcu_nmi_enter() handle nesting, as there are now some
architectures that use RCU read-side critical sections in NMI-like constructs that can nest in one another. Algorithm courtesy of Andy Lutomirski.

2. Remove redundant rcu_is_cpu_rrupt_from_idle() from tiny RCU,
courtesy of Alexander Gordeev.

3. Fix invoke_rcu_callbacks() comment to correctly reflect
required calling environment.

4. Allow 1- and 2-byte smp_load_acquire() and smp_store_release(),
given that the C11 standard requires that compilers support this.

5. Replace smp_read_barrier_depends() with lockless_dereference(),
courtesy of Pranith Kumar.

6. Directly force QS when call_rcu_[bh|sched]() on idle_task for
tiny RCU, courtesy of Lai Jiangshan. Saves more than 1KB.

7. Fix sparse warning from hlist_for_each_entry_continue_rcu_bh(),
courtesy of Ying Xue.

8. Fix hang in CPU hotplug code, courtesy of David Hildenbrand.

9. Fix rcu_barrier() race that could result in too-short wait.

10. Remove obsolete "select IRQ_WORK" from config TREE_RCU, courtesy
of Lai Jiangshan.

Thanx, Paul

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

 b/include/linux/compiler.h |    2 
 b/include/linux/rculist.h  |   16 +++---
 b/include/linux/rcupdate.h |   10 ++--
 b/init/Kconfig             |    2 
 b/kernel/cpu.c             |   56 +++++++++-------------
 b/kernel/rcu/rcu.h         |    6 ++
 b/kernel/rcu/tiny.c        |  111 +++------------------------------------------
 b/kernel/rcu/tiny_plugin.h |    2 
 b/kernel/rcu/tree.c        |   75 ++++++++++++++++++++----------
 b/kernel/rcu/tree.h        |   30 ++----------
 b/kernel/rcu/tree_plugin.h |   45 +++++++++++-------
 11 files changed, 138 insertions(+), 217 deletions(-)