rcu: Add WRITE_ONCE() to rcu_node ->boost_tasks (5822b812) · Commits · 戴 / test

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>

kernel/rcu/tree_plugin.h

+2 −2

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

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