From: Paul E. McKenney <paulmck@kernel.org>
Date: Sat, 4 Jan 2020 00:14:08 +0000 (-0800)
Subject: rcu: Add READ_ONCE() to rcu_segcblist ->tails[]
X-Git-Tag: v5.7-rc1~183^2^2^2~18
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=bfeebe24212d374f82bbf5b005371fe13acabb93;p=thirdparty%2Flinux.git

rcu: Add READ_ONCE() to rcu_segcblist ->tails[]

The rcu_segcblist structure's ->tails[] array entries are read
locklessly, so this commit adds the READ_ONCE() to a load in order to
avoid destructive compiler optimizations.

This data race was reported by KCSAN.

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

diff --git a/kernel/rcu/rcu_segcblist.c b/kernel/rcu/rcu_segcblist.c
index 5f4fd3b8777ca..426a472e73081 100644
--- a/kernel/rcu/rcu_segcblist.c
+++ b/kernel/rcu/rcu_segcblist.c
@@ -182,7 +182,7 @@ void rcu_segcblist_offload(struct rcu_segcblist *rsclp)
 bool rcu_segcblist_ready_cbs(struct rcu_segcblist *rsclp)
 {
 	return rcu_segcblist_is_enabled(rsclp) &&
-	       &rsclp->head != rsclp->tails[RCU_DONE_TAIL];
+	       &rsclp->head != READ_ONCE(rsclp->tails[RCU_DONE_TAIL]);
 }
 
 /*