Re: [PATCH v3 5/7] lib/cgroup_cpus: don't zero cpumasks in group_cpus_evenly() on allocation

Ming Lei
2023-12-13T00:56:37Z

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@gmail.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