From: "Paul E. McKenney" <paulmck@kernel.org>
Date: Fri, 3 Jan 2020 11:38:51 -0800
Subject: rcu: Add WRITE_ONCE() to rcu_node ->qsmask update
Patch-mainline: v5.7-rc1
Git-commit: 7672d647ddae37d2ea267159950bcc311e962434
References: bsc#1171828
The rcu_node structure's ->qsmask field is read locklessly, so this
commit adds the WRITE_ONCE() to an update in order to provide proper
documentation and READ_ONCE()/WRITE_ONCE() pairing.
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>
Acked-by: Daniel Wagner <dwagner@suse.de>
---
kernel/rcu/tree.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1831,7 +1831,7 @@ static void rcu_report_qs_rnp(unsigned l
WARN_ON_ONCE(oldmask); /* Any child must be all zeroed! */
WARN_ON_ONCE(!rcu_is_leaf_node(rnp) &&
rcu_preempt_blocked_readers_cgp(rnp));
- rnp->qsmask &= ~mask;
+ WRITE_ONCE(rnp->qsmask, rnp->qsmask & ~mask);
trace_rcu_quiescent_state_report(rcu_state.name, rnp->gp_seq,
mask, rnp->qsmask, rnp->level,
rnp->grplo, rnp->grphi,