From 19a5ecde086a6a5287978b12ae948fa691b197b7 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Sun, 20 Sep 2015 21:01:22 -0700 Subject: [PATCH] rcu: Suppress lockdep false positive for rcp->exp_funnel_mutex In kernels built with CONFIG_PREEMPT=y, synchronize_rcu_expedited() invokes synchronize_sched_expedited() while holding RCU-preempt's root rcu_node structure's ->exp_funnel_mutex, which is acquired after the rcu_data structure's ->exp_funnel_mutex. The first thing that synchronize_sched_expedited() will do is acquire RCU-sched's rcu_data structure's ->exp_funnel_mutex. There is no danger of an actual deadlock because the locking order is always from RCU-preempt's expedited mutexes to those of RCU-sched. Unfortunately, lockdep considers both rcu_data structures' ->exp_funnel_mutex to be in the same lock class and therefore reports a deadlock cycle. This commit silences this false positive by placing RCU-sched's rcu_data structures' ->exp_funnel_mutex locks into their own lock class. Reported-by: Sasha Levin Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 9f75f25cc5d9..775d36cc0050 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -3868,6 +3868,7 @@ static void rcu_init_new_rnp(struct rcu_node *rnp_leaf) static void __init rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp) { + static struct lock_class_key rcu_exp_sched_rdp_class; unsigned long flags; struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); struct rcu_node *rnp = rcu_get_root(rsp); @@ -3883,6 +3884,10 @@ rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp) mutex_init(&rdp->exp_funnel_mutex); rcu_boot_init_nocb_percpu_data(rdp); raw_spin_unlock_irqrestore(&rnp->lock, flags); + if (rsp == &rcu_sched_state) + lockdep_set_class_and_name(&rdp->exp_funnel_mutex, + &rcu_exp_sched_rdp_class, + "rcu_data_exp_sched"); } /* -- 2.30.2