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Subject[PATCH tip/core/rcu 16/30] rcu: Add *_ONCE() to rcu_node ->boost_kthread_status
Date
From: "Paul E. McKenney" <paulmck@kernel.org>

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: Paul E. McKenney <paulmck@kernel.org>
---
kernel/rcu/tree_plugin.h | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index b5ba148..0f8b714 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -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);
}
--
2.9.5
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