linux-kernel - Re: [PATCH] sched/numa: Fix divide by zero for sysctl_numa_balancing_scan

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Date:   Wed, 29 Mar 2023 14:28:25 -0400
From:   chris hyser <chris.hyser@...cle.com>
To:     linux-kernel@...r.kernel.org, dietmar.eggemann@....com,
        peterz@...radead.org, vincent.guittot@...aro.org
Subject: Re: [PATCH] sched/numa: Fix divide by zero for
 sysctl_numa_balancing_scan_size.

On 3/29/23 12:26, Chris Hyser wrote:
> From: chris hyser <chris.hyser@...cle.com>

Apologies. Something in my email chain put this in, but I think I 
figured it out and sent a version 1.

-chrish

> 
> 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@...cle.com>
> ---
>   kernel/sched/debug.c | 50 +++++++++++++++++++++++++++++++++++++++++++-
>   1 file changed, 49 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
> index 1637b65ba07a..dfd0fe6123ec 100644
> --- a/kernel/sched/debug.c
> +++ b/kernel/sched/debug.c
> @@ -278,6 +278,54 @@ 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)
> +{
> +	char buf[16];
> +	unsigned int scan_size;
> +
> +	if (cnt > 15)
> +		cnt = 15;
> +
> +	if (copy_from_user(&buf, ubuf, cnt))
> +		return -EFAULT;
> +	buf[cnt] = '\0';
> +
> +	if (kstrtouint(buf, 10, &scan_size))
> +		return -EINVAL;
> +
> +	if (!scan_size)
> +		return -EINVAL;
> +
> +	sysctl_numa_balancing_scan_size = scan_size;
> +
> +	*ppos += cnt;
> +	return cnt;
> +}
> +
> +static int sched_numa_scan_show(struct seq_file *m, void *v)
> +{
> +	seq_printf(m, "%d\n", sysctl_numa_balancing_scan_size);
> +	return 0;
> +}
> +
> +static int sched_numa_scan_open(struct inode *inode, struct file *filp)
> +{
> +	return single_open(filp, sched_numa_scan_show, NULL);
> +}
> +
> +static const struct file_operations sched_numa_scan_fops = {
> +	.open		= sched_numa_scan_open,
> +	.write		= sched_numa_scan_write,
> +	.read		= seq_read,
> +	.llseek		= seq_lseek,
> +	.release	= single_release,
> +};
> +
> +#endif /* CONFIG_NUMA_BALANCING */
> +
>   __read_mostly bool sched_debug_verbose;
>   
>   static const struct seq_operations sched_debug_sops;
> @@ -332,7 +380,7 @@ static __init int sched_init_debug(void)
>   	debugfs_create_u32("scan_delay_ms", 0644, numa, &sysctl_numa_balancing_scan_delay);
>   	debugfs_create_u32("scan_period_min_ms", 0644, numa, &sysctl_numa_balancing_scan_period_min);
>   	debugfs_create_u32("scan_period_max_ms", 0644, numa, &sysctl_numa_balancing_scan_period_max);
> -	debugfs_create_u32("scan_size_mb", 0644, numa, &sysctl_numa_balancing_scan_size);
> +	debugfs_create_file("scan_size_mb", 0644, numa, NULL, &sched_numa_scan_fops);
>   	debugfs_create_u32("hot_threshold_ms", 0644, numa, &sysctl_numa_balancing_hot_threshold);
>   #endif
>