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

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Date:	Tue, 12 May 2009 09:15:47 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Amerigo Wang <amwang@...hat.com>
Cc:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org
Subject: Re: [Patch] RCU trace: use scnprintf instead of snprintf

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@...ux.vnet.ibm.com>

> Signed-off-by: WANG Cong <amwang@...hat.com>
> Cc: Paul E. McKenney <paulmck@...ux.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,
--
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