From: "Paul E. McKenney" <paulmck@kernel.org>
Date: Fri, 3 Jan 2020 15:17:12 -0800
Subject: rcu: Add WRITE_ONCE() to rcu_state ->gp_req_activity
Patch-mainline: v5.7-rc1
Git-commit: 2906d2154cd6ad6e4452cc25315d3cea7bb7f2d7
References: bsc#1171828
The rcu_state structure's ->gp_req_activity 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 | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1173,7 +1173,7 @@ static bool rcu_start_this_gp(struct rcu
}
trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("Startedroot"));
WRITE_ONCE(rcu_state.gp_flags, rcu_state.gp_flags | RCU_GP_FLAG_INIT);
- rcu_state.gp_req_activity = jiffies;
+ WRITE_ONCE(rcu_state.gp_req_activity, jiffies);
if (!rcu_state.gp_kthread) {
trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("NoGPkthread"));
goto unlock_out;
@@ -1724,7 +1724,7 @@ static void rcu_gp_cleanup(void)
/* Advance CBs to reduce false positives below. */
if (!rcu_accelerate_cbs(rnp, rdp) && needgp) {
WRITE_ONCE(rcu_state.gp_flags, RCU_GP_FLAG_INIT);
- rcu_state.gp_req_activity = jiffies;
+ WRITE_ONCE(rcu_state.gp_req_activity, jiffies);
trace_rcu_grace_period(rcu_state.name,
READ_ONCE(rcu_state.gp_seq),
TPS("newreq"));