[Patch] RCU trace: use scnprintf instead of snprintf

[Amerigo Wang <amwang@redhat.com>]

snprintf can return more than the size of buffer, this case
is not expected here, obviously. Use scnprintf instead.

Signed-off-by: WANG Cong <amwang@redhat.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

---
diff --git a/kernel/rcupreempt_trace.c b/kernel/rcupreempt_trace.c
index 7c2665c..4ea4300 100644
--- a/kernel/rcupreempt_trace.c
+++ b/kernel/rcupreempt_trace.c
@@ -234,11 +234,11 @@ static ssize_t rcuctrs_read(struct file *filp, char __user *buffer,
 
 	mutex_lock(&rcupreempt_trace_mutex);
 
-	cnt += snprintf(&rcupreempt_trace_buf[cnt], RCUPREEMPT_TRACE_BUF_SIZE,
+	cnt += scnprintf(&rcupreempt_trace_buf[cnt], RCUPREEMPT_TRACE_BUF_SIZE,
 				"CPU last cur F M\n");
 	for_each_online_cpu(cpu) {
 		long *flipctr = rcupreempt_flipctr(cpu);
-		cnt += snprintf(&rcupreempt_trace_buf[cnt],
+		cnt += scnprintf(&rcupreempt_trace_buf[cnt],
 				RCUPREEMPT_TRACE_BUF_SIZE - cnt,
 					"%3d %4ld %3ld %d %d\n",
 			       cpu,
@@ -247,12 +247,12 @@ static ssize_t rcuctrs_read(struct file *filp, char __user *buffer,
 			       rcupreempt_flip_flag(cpu),
 			       rcupreempt_mb_flag(cpu));
 	}
-	cnt += snprintf(&rcupreempt_trace_buf[cnt],
+	cnt += scnprintf(&rcupreempt_trace_buf[cnt],
 			RCUPREEMPT_TRACE_BUF_SIZE - cnt,
 			"ggp = %ld, state = %s\n",
 			rcu_batches_completed(),
 			rcupreempt_try_flip_state_name());
-	cnt += snprintf(&rcupreempt_trace_buf[cnt],
+	cnt += scnprintf(&rcupreempt_trace_buf[cnt],
 			RCUPREEMPT_TRACE_BUF_SIZE - cnt,
 			"\n");
 	bcount = simple_read_from_buffer(buffer, count, ppos,