rcu: Remove remaining read-modify-write ACCESS_ONCE() calls

Change the remaining uses of ACCESS_ONCE() so that each ACCESS_ONCE() either does a load or a store, but not both.

Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

2 files changed, 9 insertions, 5 deletions

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 1b70cb6fbe3c..4b526ca46801 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1684,7 +1684,8 @@ static int rcu_gp_fqs(struct rcu_state *rsp, int fqs_state_in)
         if (ACCESS_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) {
                 raw_spin_lock_irq(&rnp->lock);
                 smp_mb__after_unlock_lock();
-                ACCESS_ONCE(rsp->gp_flags) &= ~RCU_GP_FLAG_FQS;
+                ACCESS_ONCE(rsp->gp_flags) =
+                        ACCESS_ONCE(rsp->gp_flags) & ~RCU_GP_FLAG_FQS;
                 raw_spin_unlock_irq(&rnp->lock);
         }
         return fqs_state;
@@ -2505,7 +2506,8 @@ static void force_quiescent_state(struct rcu_state *rsp)
                 raw_spin_unlock_irqrestore(&rnp_old->lock, flags);
                 return;  /* Someone beat us to it. */
         }
-        ACCESS_ONCE(rsp->gp_flags) |= RCU_GP_FLAG_FQS;
+        ACCESS_ONCE(rsp->gp_flags) =
+                ACCESS_ONCE(rsp->gp_flags) | RCU_GP_FLAG_FQS;
         raw_spin_unlock_irqrestore(&rnp_old->lock, flags);
         wake_up(&rsp->gp_wq);  /* Memory barrier implied by wake_up() path. */
 }
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index a7997e272564..218fae30c380 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -897,7 +897,8 @@ void synchronize_rcu_expedited(void)
 
         /* Clean up and exit. */
         smp_mb(); /* ensure expedited GP seen before counter increment. */
-        ACCESS_ONCE(sync_rcu_preempt_exp_count)++;
+        ACCESS_ONCE(sync_rcu_preempt_exp_count) =
+                                        sync_rcu_preempt_exp_count + 1;
 unlock_mb_ret:
         mutex_unlock(&sync_rcu_preempt_exp_mutex);
 mb_ret:
@@ -2428,8 +2429,9 @@ static int rcu_nocb_kthread(void *arg)
                         list = next;
                 }
                 trace_rcu_batch_end(rdp->rsp->name, c, !!list, 0, 0, 1);
-                ACCESS_ONCE(rdp->nocb_p_count) -= c;
-                ACCESS_ONCE(rdp->nocb_p_count_lazy) -= cl;
+                ACCESS_ONCE(rdp->nocb_p_count) = rdp->nocb_p_count - c;
+                ACCESS_ONCE(rdp->nocb_p_count_lazy) =
+                                                rdp->nocb_p_count_lazy - cl;
                 rdp->n_nocbs_invoked += c;
         }
         return 0;