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Date:   Thu, 7 Nov 2019 10:38:38 +0100 (CET)
From:   Thomas Gleixner <tglx@linutronix.de>
To:     Peter Zijlstra <peterz@infradead.org>
cc:     LKML <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@kernel.org>,
        Darren Hart <darren@dvhart.com>,
        Yi Wang <wang.yi59@zte.com.cn>,
        Yang Tao <yang.tao172@zte.com.cn>,
        Oleg Nesterov <oleg@redhat.com>,
        Florian Weimer <fweimer@redhat.com>,
        Carlos O'Donell <carlos@redhat.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>
Subject: Re: [patch 02/12] futex: Move futex exit handling into futex code
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References: <20191106215534.241796846@linutronix.de> <20191106224556.049705556@linutronix.de> <20191107092441.GC4131@hirez.programming.kicks-ass.net>
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On Thu, 7 Nov 2019, Peter Zijlstra wrote:
> 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.

Yeah. Tried to be overly smart :)