Commit 3ca3b0e2 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: Add *_ONCE() to rcu_node ->boost_kthread_status 



The rcu_node structure's ->boost_kthread_status field is accessed
locklessly, so this commit causes all updates to use WRITE_ONCE() and
all reads to use READ_ONCE().

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

Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent 2a2ae872

kernel/rcu/tree_plugin.h

+4 −4
Original line number Diff line number Diff line
@@ -1032,18 +1032,18 @@ static int rcu_boost_kthread(void *arg) 


	trace_rcu_utilization(TPS("Start boost kthread@init"));

	for (;;) {

		rnp->boost_kthread_status = RCU_KTHREAD_WAITING;

		WRITE_ONCE(rnp->boost_kthread_status, RCU_KTHREAD_WAITING);

		trace_rcu_utilization(TPS("End boost kthread@rcu_wait"));

		rcu_wait(rnp->boost_tasks || rnp->exp_tasks);

		trace_rcu_utilization(TPS("Start boost kthread@rcu_wait"));

		rnp->boost_kthread_status = RCU_KTHREAD_RUNNING;

		WRITE_ONCE(rnp->boost_kthread_status, RCU_KTHREAD_RUNNING);

		more2boost = rcu_boost(rnp);

		if (more2boost)

			spincnt++;

		else

			spincnt = 0;

		if (spincnt > 10) {

			rnp->boost_kthread_status = RCU_KTHREAD_YIELDING;

			WRITE_ONCE(rnp->boost_kthread_status, RCU_KTHREAD_YIELDING);

			trace_rcu_utilization(TPS("End boost kthread@rcu_yield"));

			schedule_timeout_interruptible(2);

			trace_rcu_utilization(TPS("Start boost kthread@rcu_yield"));
@@ -1082,7 +1082,7 @@ static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags) 
			rnp->boost_tasks = rnp->gp_tasks;

		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);

		rcu_wake_cond(rnp->boost_kthread_task,

			      rnp->boost_kthread_status);

			      READ_ONCE(rnp->boost_kthread_status));

	} else {

		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);

	}

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