[PATCH v2] sched/numa: Fix divide by zero for sysctl_numa_balancing_scan_size.

[PATCH v2] sched/numa: Fix divide by zero for sysctl_numa_balancing_scan_size.

[chris hyser]

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);
+	if (err)
+		return err;
+
+	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 +382,7 @@ 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
 
-- 
2.31.1

Re: [PATCH v2] sched/numa: Fix divide by zero for sysctl_numa_balancing_scan_size.

[Chen Yu]

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

Re: [PATCH v2] sched/numa: Fix divide by zero for sysctl_numa_balancing_scan_size.

[chris hyser]

On 4/4/23 11:32, Chen Yu wrote:
> 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?

Let me look at that. I think in general, replacing a block of code in a 
non-perf path with an existing function is better.

And thank you for looking at this.

-chrish

Re: [PATCH v2] sched/numa: Fix divide by zero for sysctl_numa_balancing_scan_size.

[chris hyser]

On 4/4/23 11:32, Chen Yu wrote:
> 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?

Yes, putting this in results in cleaner code. Thanks.

I just sent a v3 with this change.

-chrish

> 
> thanks,
> Chenyu