From: Paul E. McKenney <paulmck@kernel.org>
Date: Mon, 23 Dec 2019 03:39:35 +0000 (-0800)
Subject: srcu: Fix process_srcu()/srcu_batches_completed() datarace
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=39f91504a03a7a2abdb52205106942fa4a548d0d;p=linux.git

srcu: Fix process_srcu()/srcu_batches_completed() datarace

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@kernel.org>
---

diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 79848f7d575da..119a37319e67d 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);