linux-kernel - Re: [peterz-queue:sched/core 13/19] kernel/sched/fair.c:892:34: warning: variable 'stats' set but not used

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Message-ID: <20210911122049.GW4323@worktop.programming.kicks-ass.net>
Date:   Sat, 11 Sep 2021 14:20:49 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     kernel test robot <lkp@...el.com>
Cc:     Yafang Shao <laoar.shao@...il.com>, kbuild-all@...ts.01.org,
        linux-kernel@...r.kernel.org, linux-toolchains@...r.kernel.org
Subject: Re: [peterz-queue:sched/core 13/19] kernel/sched/fair.c:892:34:
 warning: variable 'stats' set but not used

On Sat, Sep 11, 2021 at 02:21:26AM +0800, kernel test robot wrote:

> compiler: m68k-linux-gcc (GCC) 11.2.0

>    kernel/sched/fair.c: In function 'update_curr':
>    kernel/sched/fair.c:860:42: warning: unused variable 'stats' [-Wunused-variable]
>      860 |                 struct sched_statistics *stats = __schedstats_from_se(curr);
>          |                                          ^~~~~

OK, compiler guys, this code reads like:

#define schedstats_enabled()	(0)
#define __schedstat_set(x, y)	do { } while (0)


	if (schedstats_enabled()) {
		struct sched_statistics *stats = __schedstats_from_se(curr);

		__schedstat_set(stats->exec_max,
				max(delta_exec, stats->exec_max));
	}

So yes, we initialize a variable that then isn't used, but the whole
bloody thing is inside if (0) which will not ever get ran *anyway*.

This is a crap warning if ever I saw one...