path: root/kernel/rcu/tree.c
diff options
authorPaul E. McKenney <>2015-07-19 15:13:40 -0700
committerPaul E. McKenney <>2015-08-04 08:39:21 -0700
commitaf859beaaba4d57883b08f4acbcb3974bc1f975e (patch)
tree0bff1fa9c43693c9f513daf48197be3627b3301c /kernel/rcu/tree.c
parentcdacbe1f91264687af956e810278030f2ab5a3d0 (diff)
rcu: Silence lockdep false positive for expedited grace periods
In a CONFIG_PREEMPT=y kernel, synchronize_rcu_expedited() acquires the ->exp_funnel_mutex in rcu_preempt_state, then invokes synchronize_sched_expedited, which acquires the ->exp_funnel_mutex in rcu_sched_state. There can be no deadlock because rcu_preempt_state ->exp_funnel_mutex acquisition always precedes that of rcu_sched_state. But lockdep does not know that, so it gives false-positive splats. This commit therefore associates a separate lock_class_key structure with the rcu_sched_state structure's ->exp_funnel_mutex, allowing lockdep to see the lock ordering, avoiding the false positives. Signed-off-by: Paul E. McKenney <>
Diffstat (limited to 'kernel/rcu/tree.c')
1 files changed, 10 insertions, 2 deletions
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 3af0dee2d045..439112e9d1b3 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -71,6 +71,7 @@ MODULE_ALIAS("rcutree");
static struct lock_class_key rcu_node_class[RCU_NUM_LVLS];
static struct lock_class_key rcu_fqs_class[RCU_NUM_LVLS];
static struct lock_class_key rcu_exp_class[RCU_NUM_LVLS];
+static struct lock_class_key rcu_exp_sched_class[RCU_NUM_LVLS];
* In order to export the rcu_state name to the tracing tools, it
@@ -4049,6 +4050,7 @@ static void __init rcu_init_one(struct rcu_state *rsp,
static const char * const buf[] = RCU_NODE_NAME_INIT;
static const char * const fqs[] = RCU_FQS_NAME_INIT;
static const char * const exp[] = RCU_EXP_NAME_INIT;
+ static const char * const exp_sched[] = RCU_EXP_SCHED_NAME_INIT;
static u8 fl_mask = 0x1;
int levelcnt[RCU_NUM_LVLS]; /* # nodes in each level. */
@@ -4108,8 +4110,14 @@ static void __init rcu_init_one(struct rcu_state *rsp,
- lockdep_set_class_and_name(&rnp->exp_funnel_mutex,
- &rcu_exp_class[i], exp[i]);
+ if (rsp == &rcu_sched_state)
+ lockdep_set_class_and_name(
+ &rnp->exp_funnel_mutex,
+ &rcu_exp_sched_class[i], exp_sched[i]);
+ else
+ lockdep_set_class_and_name(
+ &rnp->exp_funnel_mutex,
+ &rcu_exp_class[i], exp[i]);