linux-kernel - Re: [PATCH] sched/core: switch to BUG

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Message-ID: <20170327082440.6lvb7il66mzdaij5@hirez.programming.kicks-ass.net>
Date:   Mon, 27 Mar 2017 10:24:40 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Nicholas Mc Guire <der.herr@...r.at>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Rusty Russell <rusty@...tcorp.com.au>,
        Nick Piggin <npiggin@...e.de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched/core: switch to BUG_ON()

On Mon, Mar 27, 2017 at 09:40:46AM +0200, Nicholas Mc Guire wrote:

> Found by coccinelle: bugon.cocci
> ./kernel/sched/core.c:5913:2-5: WARNING: Use BUG_ON instead of if condition followed by BUG.

Right, so I disagree with that here.

> @@ -5909,8 +5909,8 @@ 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, non_isolated_cpus) < 0)
> -		BUG();
> +	BUG_ON(set_cpus_allowed_ptr(current, non_isolated_cpus) < 0);
> +
>  	sched_init_granularity();
>  	free_cpumask_var(non_isolated_cpus);

If the condition were without side effects, that pattern would hold, but
here the function call set_cpus_allowed_ptr() is very much not a pure
function, so wrapping it in a BUG_ON() just fels wrong.