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rcu: Silence lockdep false positive for expedited grace periods

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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 <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney
2015-07-19 15:13:40 -07:00
parent cdacbe1f91
commit af859beaab
2 changed files with 18 additions and 2 deletions
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12
kernel/rcu/tree.c
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@@ -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,
INIT_LIST_HEAD(&rnp->blkd_tasks);
rcu_init_one_nocb(rnp);
mutex_init(&rnp->exp_funnel_mutex);
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]);
}
}