rcu: Remove ACCESS_ONCE() from jiffies

Because jiffies is one of a very few variables marked "volatile", there
is no need to use ACCESS_ONCE() when accessing it.  This commit therefore
removes the redundant ACCESS_ONCE() wrappers.

Reported by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: NJosh Triplett <josh@joshtriplett.org>

kernel/rcu/torture.c

@@ -1352,7 +1352,7 @@ rcu_torture_shutdown(void *arg)
 	unsigned long jiffies_snap;
 
 	VERBOSE_PRINTK_STRING("rcu_torture_shutdown task started");
-	jiffies_snap = ACCESS_ONCE(jiffies);
+	jiffies_snap = jiffies;
 	while (ULONG_CMP_LT(jiffies_snap, shutdown_time) &&
 	       !kthread_should_stop()) {
 		delta = shutdown_time - jiffies_snap;
@@ -1361,7 +1361,7 @@ rcu_torture_shutdown(void *arg)
 				 "rcu_torture_shutdown task: %lu jiffies remaining\n",
 				 torture_type, delta);
 		schedule_timeout_interruptible(delta);
-		jiffies_snap = ACCESS_ONCE(jiffies);
+		jiffies_snap = jiffies;
 	}
 	if (kthread_should_stop()) {
 		VERBOSE_PRINTK_STRING("rcu_torture_shutdown task stopping");

kernel/rcu/tree.c

@@ -837,7 +837,7 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
 	 * to the next.  Only do this for the primary flavor of RCU.
 	 */
 	if (rdp->rsp == rcu_state &&
-	    ULONG_CMP_GE(ACCESS_ONCE(jiffies), rdp->rsp->jiffies_resched)) {
+	    ULONG_CMP_GE(jiffies, rdp->rsp->jiffies_resched)) {
 		rdp->rsp->jiffies_resched += 5;
 		resched_cpu(rdp->cpu);
 	}
@@ -847,7 +847,7 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
 
 static void record_gp_stall_check_time(struct rcu_state *rsp)
 {
-	unsigned long j = ACCESS_ONCE(jiffies);
+	unsigned long j = jiffies;
 	unsigned long j1;
 
 	rsp->gp_start = j;
@@ -1005,7 +1005,7 @@ static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
 
 	if (rcu_cpu_stall_suppress || !rcu_gp_in_progress(rsp))
 		return;
-	j = ACCESS_ONCE(jiffies);
+	j = jiffies;
 
 	/*
 	 * Lots of memory barriers to reject false positives.