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rcu: Add WRITE_ONCE() to rcu_node ->boost_tasks

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The rcu_node structure's ->boost_tasks field is read locklessly, so this
commit adds the WRITE_ONCE() to an update in order to provide proper
documentation and READ_ONCE()/WRITE_ONCE() pairing.

This data race was reported by KCSAN.  Not appropriate for backporting
due to failure being unlikely.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney 2020-01-04 10:44:41 -08:00
parent b68c614651
commit 5822b8126f
1 changed files with 2 additions and 2 deletions
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4
kernel/rcu/tree_plugin.h
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@ -505,7 +505,7 @@ rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags)
/* Snapshot ->boost_mtx ownership w/rnp->lock held. */
drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx) == t;
if (&t->rcu_node_entry == rnp->boost_tasks)
rnp->boost_tasks = np;
WRITE_ONCE(rnp->boost_tasks, np);
}
/*
@ -1082,7 +1082,7 @@ static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
rnp->qsmask == 0 &&
(ULONG_CMP_GE(jiffies, rnp->boost_time) || rcu_state.cbovld))) {
if (rnp->exp_tasks == NULL)
rnp->boost_tasks = rnp->gp_tasks;
WRITE_ONCE(rnp->boost_tasks, rnp->gp_tasks);
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
rcu_wake_cond(rnp->boost_kthread_task,
READ_ONCE(rnp->boost_kthread_status));