linux-kernel - Re: [patch 02/12] futex: Move futex exit handling into futex code

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Message-ID: <20191107092441.GC4131@hirez.programming.kicks-ass.net>
Date:   Thu, 7 Nov 2019 10:24:41 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Darren Hart <darren@...art.com>,
        Yi Wang <wang.yi59@....com.cn>,
        Yang Tao <yang.tao172@....com.cn>,
        Oleg Nesterov <oleg@...hat.com>,
        Florian Weimer <fweimer@...hat.com>,
        Carlos O'Donell <carlos@...hat.com>,
        Alexander Viro <viro@...iv.linux.org.uk>
Subject: Re: [patch 02/12] futex: Move futex exit handling into futex code

On Wed, Nov 06, 2019 at 10:55:36PM +0100, Thomas Gleixner wrote:

> -#ifdef CONFIG_FUTEX
> -	if (unlikely(tsk->robust_list)) {
> -		exit_robust_list(tsk);
> -		tsk->robust_list = NULL;
> -	}
> -#ifdef CONFIG_COMPAT
> -	if (unlikely(tsk->compat_robust_list)) {
> -		compat_exit_robust_list(tsk);
> -		tsk->compat_robust_list = NULL;
> -	}
> -#endif
> -	if (unlikely(!list_empty(&tsk->pi_state_list)))
> -		exit_pi_state_list(tsk);
> -#endif

> +void futex_mm_release(struct task_struct *tsk)
> +{
> +	if (unlikely(tsk->robust_list)) {
> +		exit_robust_list(tsk);
> +		tsk->robust_list = NULL;
> +	}
> +
> +	if (IS_ENABLED(CONFIG_COMPAT)) {
> +		if (unlikely(tsk->compat_robust_list)) {
> +			compat_exit_robust_list(tsk);
> +			tsk->compat_robust_list = NULL;
> +		}
> +	}

I suppose it is this substitution that causes the compile error mingo
found. The problem with IS_ENABLED() is that the whole block still needs
to compile (before it can be thrown out), and in this case
tsk->compat_robust_list doesn't exist.

> +
> +	if (unlikely(!list_empty(&tsk->pi_state_list)))
> +		exit_pi_state_list(tsk);
> +}