[PATCH tip/core/rcu 06/13] rcutorture: Replace barriers with smp_store_release() and smp_load_acquire()

Paul E. McKenney
2015-05-12T22:59:37Z

The rcutorture.c file uses several explicit memory barriers that can
easily be converted to smp_store_release() and smp_load_acquire(), which
improves maintainability and also improves performance a bit.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
kernel/rcu/rcutorture.c | 24 +++++++++++++-----------
1 file changed, 13 insertions(+), 11 deletions(-)

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 7294d605c481..90ff8dfc51e5 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -672,8 +672,8 @@ static void rcu_torture_boost_cb(struct rcu_head *head)
struct rcu_boost_inflight *rbip =
container_of(head, struct rcu_boost_inflight, rcu);

- smp_mb(); /* Ensure RCU-core accesses precede clearing ->inflight */
- rbip->inflight = 0;
+ /* Ensure RCU-core accesses precede clearing ->inflight */
+ smp_store_release(&rbip->inflight, 0);
}

static int rcu_torture_boost(void *arg)
@@ -710,9 +710,9 @@ static int rcu_torture_boost(void *arg)
call_rcu_time = jiffies;
while (ULONG_CMP_LT(jiffies, endtime)) {
/* If we don't have a callback in flight, post one. */
- if (!rbi.inflight) {
- smp_mb(); /* RCU core before ->inflight = 1. */
- rbi.inflight = 1;
+ if (!smp_load_acquire(&rbi.inflight)) {
+ /* RCU core before ->inflight = 1. */
+ smp_store_release(&rbi.inflight, 1);
call_rcu(&rbi.rcu, rcu_torture_boost_cb);
if (jiffies - call_rcu_time >
test_boost_duration * HZ - HZ / 2) {
@@ -751,11 +751,10 @@ checkwait: stutter_wait("rcu_torture_boost");
} while (!torture_must_stop());

/* Clean up and exit. */
- while (!kthread_should_stop() || rbi.inflight) {
+ while (!kthread_should_stop() || smp_load_acquire(&rbi.inflight)) {
torture_shutdown_absorb("rcu_torture_boost");
schedule_timeout_uninterruptible(1);
}
- smp_mb(); /* order accesses to ->inflight before stack-frame death. */
destroy_rcu_head_on_stack(&rbi.rcu);
torture_kthread_stopping("rcu_torture_boost");
return 0;
@@ -1413,12 +1412,15 @@ static int rcu_torture_barrier_cbs(void *arg)
do {
wait_event(barrier_cbs_wq[myid],
(newphase =
- READ_ONCE(barrier_phase)) != lastphase ||
+ smp_load_acquire(&barrier_phase)) != lastphase ||
torture_must_stop());
lastphase = newphase;
- smp_mb(); /* ensure barrier_phase load before ->call(). */
if (torture_must_stop())
break;
+ /*
+ * The above smp_load_acquire() ensures barrier_phase load
+ * is ordered before the folloiwng ->call().
+ */
cur_ops->call(&rcu, rcu_torture_barrier_cbf);
if (atomic_dec_and_test(&barrier_cbs_count))
wake_up(&barrier_wq);
@@ -1439,8 +1441,8 @@ static int rcu_torture_barrier(void *arg)
do {
atomic_set(&barrier_cbs_invoked, 0);
atomic_set(&barrier_cbs_count, n_barrier_cbs);
- smp_mb(); /* Ensure barrier_phase after prior assignments. */
- barrier_phase = !barrier_phase;
+ /* Ensure barrier_phase ordered after prior assignments. */
+ smp_store_release(&barrier_phase, !barrier_phase);
for (i = 0; i < n_barrier_cbs; i++)
wake_up(&barrier_cbs_wq[i]);
wait_event(barrier_wq,
--
1.8.1.5