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

Ingo Molnar
2009-09-19T06:55:57Z

* Paul E. McKenney <paulmck@linux.vnet.ibm.com> wrote:

> 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(-)

Thanks Paul, applied them to tip:core/urgent.

Ingo