linux-kernel - Re: [PATCH v3 5/7] lib/cgroup_cpus: don't zero cpumasks in group_cpus

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Date:   Wed, 13 Dec 2023 08:56:18 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     Yury Norov <yury.norov@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: Re: [PATCH v3 5/7] lib/cgroup_cpus: don't zero cpumasks in
 group_cpus_evenly() on allocation

On Mon, Dec 11, 2023 at 08:21:05PM -0800, Yury Norov wrote:
> nmsk and npresmsk are both allocated with zalloc_cpumask_var(), but they
> are initialized by copying later in the code, and so may be allocated
> uninitialized.
> 
> Signed-off-by: Yury Norov <yury.norov@...il.com>
> ---
>  lib/group_cpus.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/lib/group_cpus.c b/lib/group_cpus.c
> index cded3c8ea63b..c7fcd04c87bf 100644
> --- a/lib/group_cpus.c
> +++ b/lib/group_cpus.c
> @@ -347,10 +347,10 @@ struct cpumask *group_cpus_evenly(unsigned int numgrps)
>  	int ret = -ENOMEM;
>  	struct cpumask *masks = NULL;
>  
> -	if (!zalloc_cpumask_var(&nmsk, GFP_KERNEL))
> +	if (!alloc_cpumask_var(&nmsk, GFP_KERNEL))
>  		return NULL;

`nmsk` is actually used by __group_cpus_evenly() only, and it should be
local variable of __group_cpus_evenly(), can you move its allocation into
__group_cpus_evenly()?

>  
> -	if (!zalloc_cpumask_var(&npresmsk, GFP_KERNEL))
> +	if (!alloc_cpumask_var(&npresmsk, GFP_KERNEL))
>  		goto fail_nmsk;

The above one looks fine, especially `npresmsk` is initialized in
group_cpus_evenly() explicitly.


Thanks,
Ming