rcu: Mark ->expmask access in synchronize_rcu_expedited_wait()

This commit adds a READ_ONCE() to an access to the rcu_node structure's
->expmask field to prevent compiler mischief.  Detected by KCSAN.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index 1568c8ef185b2badccdf07560a397fd9739ad2b7..60197ea24ceb9c73a17382b3c031be7fff582557 100644 (file)
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -502,7 +502,8 @@ static void synchronize_rcu_expedited_wait(void)
                if (synchronize_rcu_expedited_wait_once(1))
                        return;
                rcu_for_each_leaf_node(rnp) {
-                       for_each_leaf_node_cpu_mask(rnp, cpu, rnp->expmask) {
+                       mask = READ_ONCE(rnp->expmask);
+                       for_each_leaf_node_cpu_mask(rnp, cpu, mask) {
                                rdp = per_cpu_ptr(&rcu_data, cpu);
                                if (rdp->rcu_forced_tick_exp)
                                        continue;