Messages in this thread Patch in this message | | | Subject | Re: [PATCH tip/core/rcu 3/3] rcu: place root rcu_node structure in separate lockdep class | From | Peter Zijlstra <> | Date | Thu, 08 Oct 2009 11:31:59 +0200 |
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On Tue, 2009-10-06 at 21:48 -0700, Paul E. McKenney wrote: > 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); > } > > /*
An alternative version that would not change any code in the !LOCKDEP case would read as:
--- kernel/rcutree.c | 4 ++++ 1 files changed, 4 insertions(+), 0 deletions(-)
diff --git a/kernel/rcutree.c b/kernel/rcutree.c index d8d9865..113f274 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1625,6 +1625,8 @@ static void __init rcu_init_levelspread(struct rcu_state *rsp) } #endif /* #else #ifdef CONFIG_RCU_FANOUT_EXACT */ +static struct lock_class_key rcu_root_class; + /* * Helper function for rcu_init() that initializes one rcu_state structure. */ @@ -1670,6 +1672,7 @@ static void __init rcu_init_one(struct rcu_state *rsp) INIT_LIST_HEAD(&rnp->blocked_tasks[1]); } } + lockdep_set_class(&rcu_get_root(rsp)->lock, &rcu_root_class); } /*
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