[Patch] RCU trace: use scnprintf instead of snprintf

[Patch] RCU trace: use scnprintf instead of snprintf

[Amerigo Wang]

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,

Re: [Patch] RCU trace: use scnprintf instead of snprintf

[Paul E. McKenney]

On Tue, May 12, 2009 at 06:04:15AM -0400, Amerigo Wang wrote:
> 
> snprintf can return more than the size of buffer, this case
> is not expected here, obviously. Use scnprintf instead.

Good catch!!!  I would welcome a simlarly careful review of the tracing
for the other RCU variants.

Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

> 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,