linux-kernel - Re: [PATCH] sched/topology: replace kzalloc() with kcalloc() in sched_init

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Message-ID: <3eaea922-0c78-414b-9609-abda0c97a13a@linux.ibm.com>
Date: Sun, 23 Feb 2025 12:49:09 +0530
From: Madadi Vineeth Reddy <vineethr@...ux.ibm.com>
To: Ethan Carter Edwards <ethan@...ancedwards.com>
Cc: Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>,
        Mel Gorman <mgorman@...e.de>, Valentin Schneider <vschneid@...hat.com>,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org,
        Markus Elfring <Markus.Elfring@....de>,
        Madadi Vineeth Reddy <vineethr@...ux.ibm.com>
Subject: Re: [PATCH] sched/topology: replace kzalloc() with kcalloc() in
 sched_init_numa()

Hi Ethan,

On 23/02/25 01:16, Ethan Carter Edwards wrote:
> We are trying to get rid of all multiplications from allocation
> functions to prevent integer overflows[1]. Here the multiplication is
> obviously safe, but using kcalloc() is more appropriate and improves
> readability. This patch has no effect on runtime behavior.
> 
> Link: https://github.com/KSPP/linux/issues/162 [1]
> Link: https://www.kernel.org/doc/html/next/process/deprecated.html#open-coded-arithmetic-in-allocator-arguments
> 
> Signed-off-by: Ethan Carter Edwards <ethan@...ancedwards.com>
> ---
>  kernel/sched/topology.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
> index c49aea8c10254dec985bba47b18f61be954d23f6..b4539b29fb36f6b2f0c5ca310620ebda29755e5c 100644
> --- a/kernel/sched/topology.c
> +++ b/kernel/sched/topology.c
> @@ -1918,7 +1918,7 @@ void sched_init_numa(int offline_node)
>  	 */
>  	sched_domains_numa_levels = 0;
>  
> -	masks = kzalloc(sizeof(void *) * nr_levels, GFP_KERNEL);
> +	masks = kcalloc(nr_levels, sizeof(void *), GFP_KERNEL);

Even though an overflow is very unlikely here, using kcalloc() improves
readability and adds a safeguard since its built-in overflow check has
minimal overhead.

Reviewed-by: Madadi Vineeth Reddy <vineethr@...ux.ibm.com>

Thanks,
Madadi Vineeth Reddy

>  	if (!masks)
>  		return;
>  
> @@ -1927,7 +1927,7 @@ void sched_init_numa(int offline_node)
>  	 * CPUs of nodes that are that many hops away from us.
>  	 */
>  	for (i = 0; i < nr_levels; i++) {
> -		masks[i] = kzalloc(nr_node_ids * sizeof(void *), GFP_KERNEL);
> +		masks[i] = kcalloc(nr_node_ids, sizeof(void *), GFP_KERNEL);
>  		if (!masks[i])
>  			return;
>  
> 
> ---
> base-commit: 5cf80612d3f72c46ad53ef5042b4c609c393122f
> change-id: 20250222-sched-kcalloc-1d5acea7249b
> 
> Best regards,