linux-kernel - [PATCH rcu 11/18] rcu: Mark lockless ->qsmask read in rcu_check_boost

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Message-Id: <20210721202127.2129660-11-paulmck@kernel.org>
Date:   Wed, 21 Jul 2021 13:21:19 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, kernel-team@...com, mingo@...nel.org,
        jiangshanlai@...il.com, akpm@...ux-foundation.org,
        mathieu.desnoyers@...icios.com, josh@...htriplett.org,
        tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org,
        dhowells@...hat.com, edumazet@...gle.com, fweisbec@...il.com,
        oleg@...hat.com, joel@...lfernandes.org,
        "Paul E. McKenney" <paulmck@...nel.org>
Subject: [PATCH rcu 11/18] rcu: Mark lockless ->qsmask read in rcu_check_boost_fail()

Accesses to ->qsmask are normally protected by ->lock, but there is an
exception in the diagnostic code in rcu_check_boost_fail().  This commit
therefore applies data_race() to this access to avoid KCSAN complaining
about the C-language writes protected by ->lock.

Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 kernel/rcu/tree_stall.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
index 42847caa3909b..6dd6c9aa3f757 100644
--- a/kernel/rcu/tree_stall.h
+++ b/kernel/rcu/tree_stall.h
@@ -766,7 +766,7 @@ bool rcu_check_boost_fail(unsigned long gp_state, int *cpup)
 
 	rcu_for_each_leaf_node(rnp) {
 		if (!cpup) {
-			if (READ_ONCE(rnp->qsmask)) {
+			if (data_race(READ_ONCE(rnp->qsmask))) {
 				return false;
 			} else {
 				if (READ_ONCE(rnp->gp_tasks))
-- 
2.31.1.189.g2e36527f23