[PATCH tip/core/rcu 05/19] rcu: Add READ_ONCE and data_race() to rcu_node ->boost_tasks

paulmck
2020-04-15T17:11:13Z

The rcu_node structure's ->boost_tasks field is read locklessly, so this
commit adds the READ_ONCE() to one load in order to avoid destructive
compiler optimizations. The other load is from a diagnostic print,
so data_race() suffices.

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 | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 35d77db..ed6bb46 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -760,7 +760,7 @@ dump_blkd_tasks(struct rcu_node *rnp, int ncheck)
pr_info("%s: %d:%d ->qsmask %#lx ->qsmaskinit %#lx ->qsmaskinitnext %#lx\n",
__func__, rnp1->grplo, rnp1->grphi, rnp1->qsmask, rnp1->qsmaskinit, rnp1->qsmaskinitnext);
pr_info("%s: ->gp_tasks %p ->boost_tasks %p ->exp_tasks %p\n",
- __func__, READ_ONCE(rnp->gp_tasks), rnp->boost_tasks,
+ __func__, READ_ONCE(rnp->gp_tasks), data_race(rnp->boost_tasks),
READ_ONCE(rnp->exp_tasks));
pr_info("%s: ->blkd_tasks", __func__);
i = 0;
@@ -1036,7 +1036,8 @@ static int rcu_boost_kthread(void *arg)
for (;;) {
WRITE_ONCE(rnp->boost_kthread_status, RCU_KTHREAD_WAITING);
trace_rcu_utilization(TPS("End boost kthread@rcu_wait"));
- rcu_wait(rnp->boost_tasks || READ_ONCE(rnp->exp_tasks));
+ rcu_wait(READ_ONCE(rnp->boost_tasks) ||
+ READ_ONCE(rnp->exp_tasks));
trace_rcu_utilization(TPS("Start boost kthread@rcu_wait"));
WRITE_ONCE(rnp->boost_kthread_status, RCU_KTHREAD_RUNNING);
more2boost = rcu_boost(rnp);
--
2.9.5