[PATCH tip/core/rcu 0/3] Cleanups/bugfixes for large systems and TREE_PREEMPT_RCU

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

This set of patches does some cleanups and fixes a bug that prevents
TREE_PREEMPT_RCU from running reliably on large systems (more than
64 CPUs, or on 32-bit systems, more than 32 CPUs).  The patches are
as follows:

1.	Add WARN_ON_ONCE() consistency checks to catch bugs.  These
	are all on slowpaths, so are appropriate for production use.

2.	Apply the results of a code walkthrough of rcutree_plugin.h.
	This includes a fix for a theoretical race that could result in
	excessively long RCU grace periods, or perhaps even hangs/OOMs.

3.	Fix a bug introduced in a bugfix commit #de078d875 that caused
	large systems to only partially initialize the fields in the
	rcu_node tree.  TREE_RCU doesn't care about any of these fields,
	which explains why only TREE_PREEMPT_RCU was broken.

With these fixes, large systems using TREE_PREEMPT_RCU pass moderate
rcutorture runs (but with Josh Triplett's mods that force frequent
preemption within RCU read-side critical sections).  I am sure that
there are more bugs, but these fixes get things much closer.

 b/kernel/rcutree.c        |   13 +++++++++----
 b/kernel/rcutree_plugin.h |   21 ++++++++++++++-------
 kernel/rcutree.c          |   38 +++++++++-----------------------------
 kernel/rcutree_plugin.h   |   16 +++++++++-------
 4 files changed, 41 insertions(+), 47 deletions(-)