[PATCH tip/core/rcu 3/3] rcu: place root rcu_node structure in separate lockdep class

Paul E. McKenney
2009-10-07T04:49:01Z

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

Before this patch, all of the rcu_node structures were in the same lockdep
class, so that lockdep would complain when rcu_preempt_offline_tasks()
acquired the root rcu_node structure's lock while holding one of the leaf
rcu_nodes' locks. This patch changes rcu_init_one() to use a separate
spin_lock_init() for the root rcu_node structure's lock than is used for
that of all of the rest of the rcu_node structures, which puts the root
rcu_node structure's lock in its own lockdep class.

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
kernel/rcutree.c | 4 +++-
1 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index d8d9865..705f02a 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1647,7 +1647,8 @@ static void __init rcu_init_one(struct rcu_state *rsp)
cpustride *= rsp->levelspread[i];
rnp = rsp->level[i];
for (j = 0; j < rsp->levelcnt[i]; j++, rnp++) {
- spin_lock_init(&rnp->lock);
+ if (rnp != rcu_get_root(rsp))
+ spin_lock_init(&rnp->lock);
rnp->gpnum = 0;
rnp->qsmask = 0;
rnp->qsmaskinit = 0;
@@ -1670,6 +1671,7 @@ static void __init rcu_init_one(struct rcu_state *rsp)
INIT_LIST_HEAD(&rnp->blocked_tasks[1]);
}
}
+ spin_lock_init(&rcu_get_root(rsp)->lock);
}

/*
--
1.5.2.5