linux-kernel - [PATCH tip/core/rcu 0/3] Cleanups/bugfixes for large systems and TREE_PREEMPT

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Date:	Fri, 18 Sep 2009 09:49:55 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	mingo@...e.hu, laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...ymtl.ca,
	josh@...htriplett.org, dvhltc@...ibm.com, niv@...ibm.com,
	tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org,
	Valdis.Kletnieks@...edu
Subject: [PATCH tip/core/rcu 0/3] Cleanups/bugfixes for large systems and
	TREE_PREEMPT_RCU

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(-)
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