[PATCH tip/core/rcu 12/18] rcutorture: Fix stray access to rcu_fwd_cb_nodelay

[paulmck]

From: "Paul E. McKenney" <paulmck@xxxxxxxxxx>

The rcu_fwd_cb_nodelay variable suppresses excessively long read-side
delays while carrying out an rcutorture forward-progress test.  As such,
it is accessed both by readers and updaters, and most of the accesses
therefore use *_ONCE().  Except for one in rcu_read_delay(), which this
commit fixes.

This data race was reported by KCSAN.  Not appropriate for backporting
due to this being rcutorture.

Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
---
 kernel/rcu/rcutorture.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index edd9746..124160a 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -339,7 +339,7 @@ rcu_read_delay(struct torture_random_state *rrsp, struct rt_read_seg *rtrsp)
 	 * period, and we want a long delay occasionally to trigger
 	 * force_quiescent_state. */
 
-	if (!rcu_fwd_cb_nodelay &&
+	if (!READ_ONCE(rcu_fwd_cb_nodelay) &&
 	    !(torture_random(rrsp) % (nrealreaders * 2000 * longdelay_ms))) {
 		started = cur_ops->get_gp_seq();
 		ts = rcu_trace_clock_local();
-- 
2.9.5