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Subject[PATCH tip/core/rcu 12/18] rcutorture: Fix stray access to rcu_fwd_cb_nodelay
Date
From: "Paul E. McKenney" <paulmck@kernel.org>

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@kernel.org>
---
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
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