rcu: Add WRITE_ONCE() to rcu_node ->boost_tasks
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>
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@ -505,7 +505,7 @@ rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags)
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/* Snapshot ->boost_mtx ownership w/rnp->lock held. */
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drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx) == t;
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if (&t->rcu_node_entry == rnp->boost_tasks)
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rnp->boost_tasks = np;
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WRITE_ONCE(rnp->boost_tasks, np);
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}
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/*
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@ -1082,7 +1082,7 @@ static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
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rnp->qsmask == 0 &&
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(ULONG_CMP_GE(jiffies, rnp->boost_time) || rcu_state.cbovld))) {
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if (rnp->exp_tasks == NULL)
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rnp->boost_tasks = rnp->gp_tasks;
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WRITE_ONCE(rnp->boost_tasks, rnp->gp_tasks);
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raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
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rcu_wake_cond(rnp->boost_kthread_task,
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READ_ONCE(rnp->boost_kthread_status));
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