linux-kernel - Re: [PATCH] sched: replace if (cond) BUG() with BUG

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Message-ID: <20210317084132.GA378908@gmail.com>
Date:   Wed, 17 Mar 2021 09:41:32 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Jiapeng Chong <jiapeng.chong@...ux.alibaba.com>
Cc:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched: replace if (cond) BUG() with BUG_ON()


* Ingo Molnar <mingo@...nel.org> wrote:

> 
> * Jiapeng Chong <jiapeng.chong@...ux.alibaba.com> wrote:
> 
> > Fix the following coccicheck warnings:
> > 
> > ./kernel/sched/core.c:8039:2-5: WARNING: Use BUG_ON instead of if
> > condition followed by BUG.
> > 
> > Reported-by: Abaci Robot <abaci@...ux.alibaba.com>
> > Signed-off-by: Jiapeng Chong <jiapeng.chong@...ux.alibaba.com>
> > ---
> >  kernel/sched/core.c | 3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> > 
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index 9819121..7392bc0 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -8035,8 +8035,7 @@ void __init sched_init_smp(void)
> >  	mutex_unlock(&sched_domains_mutex);
> >  
> >  	/* Move init over to a non-isolated CPU */
> > -	if (set_cpus_allowed_ptr(current, housekeeping_cpumask(HK_FLAG_DOMAIN)) < 0)
> > -		BUG();
> > +	BUG(set_cpus_allowed_ptr(current, housekeeping_cpumask(HK_FLAG_DOMAIN)) < 0);
> 
> The patch doesn't quite do what the title & changelog claims...

More importantly, we use this pattern when we don't want !CONFIG_BUG 
to remove the 'condition'.

I.e. the "side effect" here is important scheduler logic. It must 
never be optimized out.

Thanks,

	Ingo