Re: [PATCH] sched_ext: fix uninitialized ret on alloc_percpu() failure

[Andrea Righi <arighi@nvidia.com>]

On Tue, Dec 16, 2025 at 05:39:55PM +0800, Liang Jie wrote:
> From: Liang Jie <liangjie@lixiang.com>
> 
> Smatch reported:
> 
>   kernel/sched/ext.c:5332 scx_alloc_and_add_sched() warn: passing zero to 'ERR_PTR'
> 
> In scx_alloc_and_add_sched(), the alloc_percpu() failure path jumps to
> err_free_gdsqs without initializing @ret. That can lead to returning
> ERR_PTR(0), which violates the ERR_PTR() convention and confuses
> callers.
> 
> Set @ret to -ENOMEM before jumping to the error path when
> alloc_percpu() fails.
> 
> Reported-by: kernel test robot <lkp@intel.com>
> Closes: https://lore.kernel.org/r/202512141601.yAXDAeA9-lkp@intel.com/
> Reported-by: Dan Carpenter <error27@gmail.com>
> Fixes: c201ea1578d3 ("sched_ext: Move event_stats_cpu into scx_sched")
> Signed-off-by: Liang Jie <liangjie@lixiang.com>

Makes sense to me, good catch.

Reviewed-by: Andrea Righi <arighi@nvidia.com>

Thanks,
-Andrea

> ---
>  kernel/sched/ext.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
> index 05f5a49e9649..8ea243b04dc9 100644
> --- a/kernel/sched/ext.c
> +++ b/kernel/sched/ext.c
> @@ -4761,8 +4761,10 @@ static struct scx_sched *scx_alloc_and_add_sched(struct sched_ext_ops *ops)
>  	}
>  
>  	sch->pcpu = alloc_percpu(struct scx_sched_pcpu);
> -	if (!sch->pcpu)
> +	if (!sch->pcpu) {
> +		ret = -ENOMEM;
>  		goto err_free_gdsqs;
> +	}
>  
>  	sch->helper = kthread_run_worker(0, "sched_ext_helper");
>  	if (IS_ERR(sch->helper)) {
> -- 
> 2.25.1
>