linux-kernel - Re: [PATCH v1] sched/fair: Fix memory leak in alloc_fair_sched

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Message-ID: <d99ce13a-3b27-46c8-9d65-99cf979f537f@amd.com>
Date: Tue, 24 Jun 2025 10:01:22 +0530
From: K Prateek Nayak <kprateek.nayak@....com>
To: Zihuan Zhang <zhangzihuan@...inos.cn>
Cc: linux-kernel@...r.kernel.org, mingo@...hat.com, peterz@...radead.org,
 juri.lelli@...hat.com, vincent.guittot@...aro.org, dietmar.eggemann@....com,
 rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de, vschneid@...hat.com
Subject: Re: [PATCH v1] sched/fair: Fix memory leak in
 alloc_fair_sched_group()

On 6/23/2025 11:49 AM, Zihuan Zhang wrote:
> alloc_fair_sched_group() allocates per-CPU cfs_rq[] and se[] arrays
> for a task group. However, if either allocation fails, or a per-CPU
> allocation fails during the loop, the function may leak memory.

alloc_fair_sched_group() is only called by sched_create_group()
which does a sched_free_group() on failure that calls
free_fair_sched_group(). I don't see the memory leak in this scenario.
What am I missing?

> This patch fixes the memory leak by:
> - Using sizeof(*ptr) instead of sizeof(ptr) for correctness.
> - Using the existing free_fair_sched_group() function to clean up
> Note: Calling free_fair_sched_group() unconditionally in the failure
> path is safe, as kfree(NULL) is a no-op in the kernel. This avoids
> duplicating cleanup logic and improves robustness.
> 
> Signed-off-by: Zihuan Zhang <zhangzihuan@...inos.cn>
> ---
>   kernel/sched/fair.c | 10 +++++-----
>   1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 7a14da5396fb..920174245517 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -13372,12 +13372,12 @@ int alloc_fair_sched_group(struct task_group *tg, struct task_group *parent)
>   	struct cfs_rq *cfs_rq;>   	int i;
>   
> -	tg->cfs_rq = kcalloc(nr_cpu_ids, sizeof(cfs_rq), GFP_KERNEL);
> +	tg->cfs_rq = kcalloc(nr_cpu_ids, sizeof(*tg->cfs_rq), GFP_KERNEL);
>   	if (!tg->cfs_rq)
>   		goto err;
> -	tg->se = kcalloc(nr_cpu_ids, sizeof(se), GFP_KERNEL);
> +	tg->se = kcalloc(nr_cpu_ids, sizeof(*tg->se), GFP_KERNEL);
>   	if (!tg->se)
> -		goto err;
> +		goto err_free_rq;
>   
>   	tg->shares = NICE_0_LOAD;
>   
> @@ -13387,7 +13387,7 @@ int alloc_fair_sched_group(struct task_group *tg, struct task_group *parent)
>   		cfs_rq = kzalloc_node(sizeof(struct cfs_rq),
>   				      GFP_KERNEL, cpu_to_node(i));
>   		if (!cfs_rq)
> -			goto err;
> +			goto err_free_rq;
>   
>   		se = kzalloc_node(sizeof(struct sched_entity_stats),
>   				  GFP_KERNEL, cpu_to_node(i));
> @@ -13402,7 +13402,7 @@ int alloc_fair_sched_group(struct task_group *tg, struct task_group *parent)
>   	return 1;
>   
>   err_free_rq:
> -	kfree(cfs_rq);

This will actually introducing a memory leak. If allocation of "se"
fails, the "cfs_rq" won't be linked to "tg" and needs to be freed here.

> +	free_fair_sched_group(tg);

free_fair_sched_group() doesn't NULL out the "tg->cfs_rq" and "tg->se"
after freeing them which now introduces double-free via
free_fair_sched_group() on failure in alloc_fair_sched_group().

>   err:
>   	return 0;
>   }

-- 
Thanks and Regards,
Prateek