linux-kernel - Re: [PATCH] kthread: Fix build warning variable 'ret' set but not used

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Message-ID: <202502040714.0E55ACBDDB@keescook>
Date: Tue, 4 Feb 2025 07:15:41 -0800
From: Kees Cook <kees@...nel.org>
To: Dhruva Gole <d-gole@...com>
Cc: Frederic Weisbecker <frederic@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Vlastimil Babka <vbabka@...e.cz>, Chen Yu <yu.c.chen@...el.com>,
	linux-kernel@...r.kernel.org, Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [PATCH] kthread: Fix build warning variable 'ret' set but not
 used

On Tue, Feb 04, 2025 at 02:38:38PM +0530, Dhruva Gole wrote:
> Fix the following build time warning in kthread:
> 
>    kernel/kthread.c: In function 'kthread_affine_preferred':
> >> kernel/kthread.c:861:13: warning: variable 'ret' set but not used [-Wunused-but-set-variable]
>      861 |         int ret;
>          |             ^~~
> 
> Reported-by: kernel test robot <lkp@...el.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202501301528.t0cZVbnq-lkp@intel.com/
> Signed-off-by: Dhruva Gole <d-gole@...com>
> ---
>  kernel/kthread.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/kernel/kthread.c b/kernel/kthread.c
> index 4005b13ebd7f..f730b1413d13 100644
> --- a/kernel/kthread.c
> +++ b/kernel/kthread.c
> @@ -859,7 +859,6 @@ int kthread_affine_preferred(struct task_struct *p, const struct cpumask *mask)
>  	struct kthread *kthread = to_kthread(p);
>  	cpumask_var_t affinity;
>  	unsigned long flags;
> -	int ret;
>  
>  	if (!wait_task_inactive(p, TASK_UNINTERRUPTIBLE) || kthread->started) {
>  		WARN_ON(1);
> @@ -873,7 +872,6 @@ int kthread_affine_preferred(struct task_struct *p, const struct cpumask *mask)
>  
>  	kthread->preferred_affinity = kzalloc(sizeof(struct cpumask), GFP_KERNEL);
>  	if (!kthread->preferred_affinity) {
> -		ret = -ENOMEM;
>  		goto out;
>  	}

This seems wrong? This is an error path, so removing this causes "return
0" to happen. I would take a look at the commit history to figure out
when this mistake was introduced and adjust it correctly. I would have
expected "int ret = 0;", and "return ret;" at "out:" to be the fix.

-- 
Kees Cook