linux-kernel - Re: [PATCH -next] sched: Use struct_size() helper in task_numa

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Message-ID: <20220106113911.6ffb7fd0@gandalf.local.home>
Date:   Thu, 6 Jan 2022 11:39:11 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Xiu Jianfeng <xiujianfeng@...wei.com>
Cc:     <mingo@...hat.com>, <peterz@...radead.org>,
        <juri.lelli@...hat.com>, <vincent.guittot@...aro.org>,
        <dietmar.eggemann@....com>, <bsegall@...gle.com>,
        <mgorman@...e.de>, <bristot@...hat.com>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -next] sched: Use struct_size() helper in
 task_numa_group()

On Tue, 21 Dec 2021 21:21:38 +0800
Xiu Jianfeng <xiujianfeng@...wei.com> wrote:

> Make use of struct_size() helper instead of an open-coded calculation.
> There is no functional change in this patch.

I'm all for this clean up, but...

> 
> Link: https://github.com/KSPP/linux/issues/160
> Signed-off-by: Xiu Jianfeng <xiujianfeng@...wei.com>
> ---
>  kernel/sched/fair.c | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 095b0aa378df..265e37be0c92 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -2437,11 +2437,8 @@ static void task_numa_group(struct task_struct *p, int cpupid, int flags,
>  	int i;
>  
>  	if (unlikely(!deref_curr_numa_group(p))) {
> -		unsigned int size = sizeof(struct numa_group) +
> -				    NR_NUMA_HINT_FAULT_STATS *
> -				    nr_node_ids * sizeof(unsigned long);
> -
> -		grp = kzalloc(size, GFP_KERNEL | __GFP_NOWARN);
> +		grp = kzalloc(struct_size(grp, faults, NR_NUMA_HINT_FAULT_STATS * nr_node_ids),
> +			      GFP_KERNEL | __GFP_NOWARN);

Ug, the above is so ugly. Why remove the size variable?

		unsigned int size  = struct_size(grp, faults,
					         NR_NUMA_HINT_FAULT_STATS * nr_node_ids);

-- Steve


>  		if (!grp)
>  			return;
>