rcu: Add ACCESS_ONCE() to ->n_force_qs_lh accesses

The ->n_force_qs_lh field is accessed without the benefit of any
synchronization, so this commit adds the needed ACCESS_ONCE() wrappers.
Yes, increments to ->n_force_qs_lh can be lost, but contention should
be low and the field is strictly statistical in nature, so this is not
a problem.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

2 files changed, 3 insertions, 3 deletions

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index b3d116cd072d..e64157798624 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2304,7 +2304,7 @@ static void force_quiescent_state(struct rcu_state *rsp)
                 if (rnp_old != NULL)
                         raw_spin_unlock(&rnp_old->fqslock);
                 if (ret) {
-                        rsp->n_force_qs_lh++;
+                        ACCESS_ONCE(rsp->n_force_qs_lh)++;
                         return;
                 }
                 rnp_old = rnp;
@@ -2316,7 +2316,7 @@ static void force_quiescent_state(struct rcu_state *rsp)
         smp_mb__after_unlock_lock();
         raw_spin_unlock(&rnp_old->fqslock);
         if (ACCESS_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) {
-                rsp->n_force_qs_lh++;
+                ACCESS_ONCE(rsp->n_force_qs_lh)++;
                 raw_spin_unlock_irqrestore(&rnp_old->lock, flags);
                 return;  /* Someone beat us to it. */
         }
diff --git a/kernel/rcu/tree_trace.c b/kernel/rcu/tree_trace.c
index 4def475336d4..d1f1e64a6d72 100644
--- a/kernel/rcu/tree_trace.c
+++ b/kernel/rcu/tree_trace.c
@@ -273,7 +273,7 @@ static void print_one_rcu_state(struct seq_file *m, struct rcu_state *rsp)
         seq_printf(m, "nfqs=%lu/nfqsng=%lu(%lu) fqlh=%lu oqlen=%ld/%ld\n",
                    rsp->n_force_qs, rsp->n_force_qs_ngp,
                    rsp->n_force_qs - rsp->n_force_qs_ngp,
-                   rsp->n_force_qs_lh, rsp->qlen_lazy, rsp->qlen);
+                   ACCESS_ONCE(rsp->n_force_qs_lh), rsp->qlen_lazy, rsp->qlen);
         for (rnp = &rsp->node[0]; rnp - &rsp->node[0] < rcu_num_nodes; rnp++) {
                 if (rnp->level != level) {
                         seq_puts(m, "\n");