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@xxxxxxxxxx>
> > ---
> >   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