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From: Segher Boessenkool <segher@kernel.crashing.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: kernel test robot <lkp@intel.com>,
	Yafang Shao <laoar.shao@gmail.com>,
	kbuild-all@lists.01.org, linux-kernel@vger.kernel.org,
	linux-toolchains@vger.kernel.org
Subject: Re: [peterz-queue:sched/core 13/19] kernel/sched/fair.c:892:34: warning: variable 'stats' set but not used
Date: Sat, 11 Sep 2021 16:30:41 -0500	[thread overview]
Message-ID: <20210911213041.GD1583@gate.crashing.org> (raw)
In-Reply-To: <20210911122049.GW4323@worktop.programming.kicks-ass.net>

Hi!

On Sat, Sep 11, 2021 at 02:20:49PM +0200, Peter Zijlstra wrote:
> 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...

Yes, we really should warn "do not use a preprocessor macro if what you
want is a function"?  The variable really *is* unused, with this macro.

If we would remove dead code before warning about unused variables
there would be many *more* false positives, fwiw.


Segher

WARNING: multiple messages have this Message-ID (diff)
From: Segher Boessenkool <segher@kernel.crashing.org>
To: kbuild-all@lists.01.org
Subject: Re: [peterz-queue:sched/core 13/19] kernel/sched/fair.c:892:34: warning: variable 'stats' set but not used
Date: Sat, 11 Sep 2021 16:30:41 -0500	[thread overview]
Message-ID: <20210911213041.GD1583@gate.crashing.org> (raw)
In-Reply-To: <20210911122049.GW4323@worktop.programming.kicks-ass.net>

[-- Attachment #1: Type: text/plain, Size: 1301 bytes --]

Hi!

On Sat, Sep 11, 2021 at 02:20:49PM +0200, Peter Zijlstra wrote:
> 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...

Yes, we really should warn "do not use a preprocessor macro if what you
want is a function"?  The variable really *is* unused, with this macro.

If we would remove dead code before warning about unused variables
there would be many *more* false positives, fwiw.


Segher

  reply	other threads:[~2021-09-11 21:35 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-10 18:21 [peterz-queue:sched/core 13/19] kernel/sched/fair.c:892:34: warning: variable 'stats' set but not used kernel test robot
2021-09-10 18:21 ` kernel test robot
2021-09-11  1:46 ` Yafang Shao
2021-09-11  1:46   ` Yafang Shao
2021-09-11 12:20 ` Peter Zijlstra
2021-09-11 12:20   ` Peter Zijlstra
2021-09-11 21:30   ` Segher Boessenkool [this message]
2021-09-11 21:30     ` Segher Boessenkool
2021-09-11 22:33     ` Peter Zijlstra
2021-09-11 22:33       ` Peter Zijlstra

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