Commit 19a5ecde authored Sep 20, 2015 by Paul E. McKenney

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 <sasha.levin@oracle.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

parent 66e8c57d

kernel/rcu/tree.c

+5 −0

Original line number	Diff line number	Diff line
		@@ -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");
		}

		/*

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