linux-kernel - Re: [PATCH] sched: remove unused cpumask variable in mm_cid

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Message-ID: <20251014103439.GU3245006@noisy.programming.kicks-ass.net>
Date: Tue, 14 Oct 2025 12:34:39 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: Breno Leitao <leitao@...ian.org>,
	Kriish Sharma <kriish.sharma2006@...il.com>,
	Ingo Molnar <mingo@...hat.com>, Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>,
	linux-kernel@...r.kernel.org, david.hunter.linux@...il.com,
	skhan@...uxfoundation.org, Menglong Dong <menglong8.dong@...il.com>
Subject: Re: [PATCH] sched: remove unused cpumask variable in mm_cid_get()

On Tue, Oct 14, 2025 at 12:13:23PM +0200, Vlastimil Babka wrote:
> On 10/14/25 11:56, Breno Leitao wrote:
> > On Thu, Oct 09, 2025 at 07:48:18PM +0000, Kriish Sharma wrote:
> >> The variable 'cpumask' in mm_cid_get() was assigned but never used,
> >> causing the following build error with -Werror:
> >> 
> >> kernel/sched/sched.h: In function ‘mm_cid_get’:
> >> kernel/sched/sched.h:3743:25: error: variable ‘cpumask’ set but not used [-Werror=unused-but-set-variable]
> >>  3743 |         struct cpumask *cpumask;
> >>       |                         ^~~~~~~
> > 
> > Thanks for the fix. I am hitting the same issue in my builds.
> 
> Let me add why this years old small issue became much more problematic in
> 6.18-rc1. When I want to test my own files I'm developing on with e.g. "make
> W=1 mm/slub.o", the W=1 hits earlier in:
> 
>   CC      kernel/sched/rq-offsets.s
> In file included from kernel/sched/rq-offsets.c:5:
> kernel/sched/sched.h:3718:18: error: variable 'cpumask' set but not used
> [-Werror,-Wunused-but-set-variable]
>  3718 |         struct cpumask *cpumask;
>       |                         ^
> 1 error generated.
> make[2]: *** [scripts/Makefile.build:182: kernel/sched/rq-offsets.s] Error 1
> 
> So I can't get to the part where I test-compile my own code with W=1. So
> fixing this ASAP in 6.18 would be appreciated, thanks!
> 
> FWIW I've bisected this to commit
> 378b7708194f ("sched: Make migrate_{en,dis}able() inline")

People using W=1 and WERROR can keep the pieces. Anyway, this is a much
more coherent explanation that the original patch.