linux-kernel - Re: [PATCH v2 1/4] mm/mempolicy: Fix memory leaks in mempolicy_sysfs

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Message-ID: <Z9Gs8i1FhJJ0eaiA@gourry-fedora-PF4VCD3F>
Date: Wed, 12 Mar 2025 11:49:06 -0400
From: Gregory Price <gourry@...rry.net>
To: Rakie Kim <rakie.kim@...com>
Cc: akpm@...ux-foundation.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, linux-cxl@...r.kernel.org,
	joshua.hahnjy@...il.com, dan.j.williams@...el.com,
	ying.huang@...ux.alibaba.com, kernel_team@...ynix.com,
	honggyu.kim@...com, yunjeong.mun@...com
Subject: Re: [PATCH v2 1/4] mm/mempolicy: Fix memory leaks in
 mempolicy_sysfs_init()

On Wed, Mar 12, 2025 at 04:56:24PM +0900, Rakie Kim wrote:
> Improper cleanup of sysfs attributes caused kobject and memory leaks when
> initialization failed or nodes were removed.
> 
> This patch ensures proper deallocation of kobjects and memory, preventing
> resource leaks and improving stability.
>

This patch does multiple things, please split these changes into
multiple patches.

> Fixes: dce41f5ae253 ("mm/mempolicy: implement the sysfs-based weighted_interleave interface")
> Signed-off-by: Rakie Kim <rakie.kim@...com>
> ---
>  mm/mempolicy.c | 29 +++++++++++++++--------------
>  1 file changed, 15 insertions(+), 14 deletions(-)
> 
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index bbaadbeeb291..1691748badb2 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -3541,39 +3541,40 @@ static int __init mempolicy_sysfs_init(void)
>  	int err;
>  	static struct kobject *mempolicy_kobj;
>  
> -	mempolicy_kobj = kzalloc(sizeof(*mempolicy_kobj), GFP_KERNEL);
> -	if (!mempolicy_kobj) {
> +	node_attrs = kcalloc(nr_node_ids, sizeof(struct iw_node_attr *),
> +			     GFP_KERNEL);
> +	if (!node_attrs) {
>  		err = -ENOMEM;
>  		goto err_out;
>  	}
>  
> -	node_attrs = kcalloc(nr_node_ids, sizeof(struct iw_node_attr *),
> -			     GFP_KERNEL);
> -	if (!node_attrs) {
> +	mempolicy_kobj = kzalloc(sizeof(*mempolicy_kobj), GFP_KERNEL);
> +	if (!mempolicy_kobj) {
>  		err = -ENOMEM;
> -		goto mempol_out;
> +		goto node_out;
>  	}

It's not clear to me why you re-ordered these allocations, it seems
superfluous.

>  
>  	err = kobject_init_and_add(mempolicy_kobj, &mempolicy_ktype, mm_kobj,
>  				   "mempolicy");
> -	if (err)
> -		goto node_out;
> +	if (err) {
> +		kobject_put(mempolicy_kobj);

Is this correct? If kobject_init_and_add fails, from other examples we
need only free the mempolicy_kobj - because it failed to initialize and
therefore should not have any references.  I think this causes an
underflow.

> +		goto err_out;
> +	}
>  
>  	err = add_weighted_interleave_group(mempolicy_kobj);
>  	if (err) {
> -		pr_err("mempolicy sysfs structure failed to initialize\n");
>  		kobject_put(mempolicy_kobj);
> -		return err;
> +		goto err_out;
>  	}
>  
> -	return err;
> +	return 0;
> +

Please keep functional changes and refactors separate.  There's more
churn in this patch than is needed to accomplish what the changelog
states is the intent.

>  node_out:
>  	kfree(node_attrs);
> -mempol_out:
> -	kfree(mempolicy_kobj);
>  err_out:
> -	pr_err("failed to add mempolicy kobject to the system\n");
> +	pr_err("mempolicy sysfs structure failed to initialize\n");
>  	return err;
> +
>  }
>  
>  late_initcall(mempolicy_sysfs_init);
> 
> base-commit: 80e54e84911a923c40d7bee33a34c1b4be148d7a
> -- 
> 2.34.1
>