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Date:   Tue, 4 Apr 2023 23:32:48 +0800
From:   Chen Yu <yu.c.chen@intel.com>
To:     chris hyser <chris.hyser@oracle.com>
CC:     <linux-kernel@vger.kernel.org>, <dietmar.eggemann@arm.com>,
        <peterz@infradead.org>, <vincent.guittot@linaro.org>
Subject: Re: [PATCH v2] sched/numa: Fix divide by zero for
 sysctl_numa_balancing_scan_size.
Message-ID: <ZCxDICwfUojWTGr5@chenyu5-mobl1>
References: <20230330150757.547423-1-chris.hyser@oracle.com>
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On 2023-03-30 at 11:07:57 -0400, chris hyser wrote:
> Commit 6419265899d9 ("sched/fair: Fix division by zero
> sysctl_numa_balancing_scan_size") prevented a divide by zero by using
> sysctl mechanisms to return EINVAL for a sysctl_numa_balancing_scan_size
> value of zero. When moved from a sysctl to a debugfs file, this checking
> was lost.
> 
> This patch puts zero checking back in place.
> 
> Signed-off-by: Chris Hyser <chris.hyser@oracle.com>
> ---
>  kernel/sched/debug.c | 52 +++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 51 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
> index 1637b65ba07a..b5fc7e250128 100644
> --- a/kernel/sched/debug.c
> +++ b/kernel/sched/debug.c
> @@ -278,6 +278,56 @@ static const struct file_operations sched_dynamic_fops = {
>  
>  #endif /* CONFIG_PREEMPT_DYNAMIC */
>  
> +#ifdef CONFIG_NUMA_BALANCING
> +
> +static ssize_t sched_numa_scan_write(struct file *filp, const char __user *ubuf,
> +				     size_t cnt, loff_t *ppos)
> +{
> +	int err;
> +	char buf[16];
> +	unsigned int scan_size;
> +
> +	if (cnt > 15)
> +		cnt = 15;
> +
> +	if (copy_from_user(&buf, ubuf, cnt))
> +		return -EFAULT;
> +	buf[cnt] = '\0';
> +
> +	err = kstrtouint(buf, 10, &scan_size);
While testing the code, it is found that there is a
kstrtouint_from_user() could do the above. Not sure
if it is worthy to use that?

thanks,
Chenyu