[PATCH tip/core/rcu 0/3] rcu: prevent hangs by simplifying rcu_barrier/CPU-hotplug, fix lockdep complaint

Paul E. McKenney
2009-10-07T04:48:30Z

This patchset fixes a couple of issues with TREE_PREEMPT_RCU:

1. The current implementation of rcu_barrier() waits for any
prior CPU-hotplug operation to complete. This code path has
resulted in some hangs, so first move this code from rcupdate.c
to rcutree.c and then use a simpler algorithm that avoids the
waiting, eliminating the possibility of such hangs.

2. The lockdep facility complains from time to time due to the
fact that certain combinations of CPU-hotplug operations can
cause the TREE_PREEMPT_RCU code to acquire the root rcu_node
structure's lock while holding a leaf rcu_node structure's
lock. This patch places the root rcu_node structure's lock
into its own lockdep class to prevent this false positive.

Ingo, please rewind tip/core/rcu to commit #135c8aea before applying this
series, as these patches really need to go into 2.6.32. Reworked and
retested rcutiny (for 2.6.33, as Linus requested) will follow in a
few days. Or more patches for more bug fixes, as the case may be. ;-)

b/kernel/rcupdate.c | 120 -----------------------------------
b/kernel/rcutree.c | 120 +++++++++++++++++++++++++++++++++++
b/kernel/rcutree.h | 11 ++-
b/kernel/rcutree_plugin.h | 34 ++++++++++
b/kernel/rcutree_trace.c | 5 -
kernel/rcutree.c | 156 ++++++++++++++++++++++++----------------------
6 files changed, 248 insertions(+), 198 deletions(-)