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

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Message-ID: <20250204155053.7tthci4fyamo37lz@lcpd911>
Date: Tue, 4 Feb 2025 21:20:53 +0530
From: Dhruva Gole <d-gole@...com>
To: Kees Cook <kees@...nel.org>
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 Feb 04, 2025 at 07:15:41 -0800, Kees Cook wrote:
> 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.

Seems like it was introduced in commit 4d13f4304fa43 ("kthread: Implement preferred affinity")

This was a bit wrong to begin with. But you're right I will follow your
suggestion and send out a v2.

-- 
Best regards,
Dhruva Gole
Texas Instruments Incorporated