linux-kernel - Re: [patch 58/63] futex: Prevent requeue

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Message-ID: <878s1j3odt.ffs@tglx>
Date:   Mon, 02 Aug 2021 16:35:58 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Will Deacon <will@...nel.org>,
        Waiman Long <longman@...hat.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Davidlohr Bueso <dave@...olabs.net>
Subject: Re: [patch 58/63] futex: Prevent requeue_pi() lock nesting issue on RT

On Mon, Aug 02 2021 at 15:10, Peter Zijlstra wrote:

> On Mon, Aug 02, 2021 at 02:56:09PM +0200, Peter Zijlstra wrote:
>>  static inline int futex_requeue_pi_wakeup_sync(struct futex_q *q)
>>  {
>> +	int old, new;
>>  
>> +	old = atomic_read_acquire(&q->requeue_state);
>> +	do {
>>  		/* Is requeue done already? */
>> +		if (old >= Q_REQUEUE_PI_DONE)
>>  			break;
>
> I think that can be: return old; for slightly simpler code.

Yes.