[PATCH tip/core/rcu 3/4] srcu: Fix process_srcu()/srcu_batches_completed() datarace

[paulmck]

From: "Paul E. McKenney" <paulmck@xxxxxxxxxx>

The srcu_struct structure's ->srcu_idx field is accessed locklessly,
so reads must use READ_ONCE().  This commit therefore adds the needed
READ_ONCE() invocation where it was missed.

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

Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
---
 kernel/rcu/srcutree.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 79848f7d..119a373 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -1079,7 +1079,7 @@ EXPORT_SYMBOL_GPL(srcu_barrier);
  */
 unsigned long srcu_batches_completed(struct srcu_struct *ssp)
 {
-	return ssp->srcu_idx;
+	return READ_ONCE(ssp->srcu_idx);
 }
 EXPORT_SYMBOL_GPL(srcu_batches_completed);
 
-- 
2.9.5