Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 19a5ecde authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

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: default avatarSasha Levin <sasha.levin@oracle.com>
Signed-off-by: default avatarPaul 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");

}



/*