linux-kernel - Re: [tip:sched/core 3/19] kernel/sched/fair.c:7263 find_energy_efficient_cpu() error: uninitialized symbol 'util

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Message-ID: <Y3H7AcgnGMq5p+nn@kadam>
Date:   Mon, 14 Nov 2022 11:23:29 +0300
From:   Dan Carpenter <error27@...il.com>
To:     Qais Yousef <qyousef@...alina.io>
Cc:     oe-kbuild@...ts.linux.dev, Qais Yousef <qais.yousef@....com>,
        lkp@...el.com, oe-kbuild-all@...ts.linux.dev,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [tip:sched/core 3/19] kernel/sched/fair.c:7263
 find_energy_efficient_cpu() error: uninitialized symbol 'util_min'.

On Sat, Nov 12, 2022 at 05:47:05PM +0000, Qais Yousef wrote:
> On 11/12/22 13:16, Dan Carpenter wrote:
> > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git sched/core
> > head:   52b33d87b9197c51e8ffdc61873739d90dd0a16f
> > commit: 244226035a1f9b2b6c326e55ae5188fab4f428cb [3/19] sched/uclamp: Fix fits_capacity() check in feec()
> > config: riscv-randconfig-m031-20221111
> > compiler: riscv64-linux-gcc (GCC) 12.1.0
> > 
> > If you fix the issue, kindly add following tag where applicable
> > | Reported-by: kernel test robot <lkp@...el.com>
> > | Reported-by: Dan Carpenter <error27@...il.com>
> > 
> > smatch warnings:
> > kernel/sched/fair.c:7263 find_energy_efficient_cpu() error: uninitialized symbol 'util_min'.
> > kernel/sched/fair.c:7263 find_energy_efficient_cpu() error: uninitialized symbol 'util_max'.
> > 
> > vim +/util_min +7263 kernel/sched/fair.c
> 
> [...]
> 
> > util_min/max not initialized if uclamp_is_used() is false.  (I thought
> > I had reported this earlier but I don't see it on vger).
> 
> Thanks Dan!
> 
> It's harmless since util_min/max are ignored in util_fits_cpu() too;
> uclamp_is_used() is checked there as well.
> 
> I couldn't reproduce, I need to get GCC 12.1.0, but the below ought to cure it.
> Let me test it a bit more and send a patch.

In that case it's fine.  This is inlined.  I guess, generally, we are
going to only consider passing uninitialized variables to functions as
bugs when the functions are not inlined.  I believe that one of the
KMsan things will trigger a warning at runtime for this as well but it's
the same situation, where it's considered a false positive because it's
inlined.  (Technically it's undefined behavior either way according to
the C standard, but the standard is sometimes useless).

It's not a GCC warning, it's from Smatch.

GCC uninitialized warnings were disabled by defualt because they have
too many false positives.  Use "make W=2" to enable them.  GCC will
complain.

regards,
dan carpenter