linux-kernel - Re: [PATCH v3 7/7] locking/rtmutex: Acquire the hb lock via trylock after wait-proxylock.

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Message-ID: <20230912112643.R4IrwXEB@linutronix.de>
Date:   Tue, 12 Sep 2023 13:26:43 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, tglx@...utronix.de,
        boqun.feng@...il.com, bristot@...hat.com, bsegall@...gle.com,
        dietmar.eggemann@....com, jstultz@...gle.com,
        juri.lelli@...hat.com, longman@...hat.com, mgorman@...e.de,
        mingo@...hat.com, rostedt@...dmis.org, swood@...hat.com,
        vincent.guittot@...aro.org, vschneid@...hat.com, will@...nel.org
Subject: Re: [PATCH v3 7/7] locking/rtmutex: Acquire the hb lock via trylock
 after wait-proxylock.

On 2023-09-12 12:57:45 [+0200], Peter Zijlstra wrote:
> > --- a/kernel/futex/pi.c
> > +++ b/kernel/futex/pi.c
> > @@ -1147,19 +1143,34 @@ int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
…
> > +		rt_waiter = rt_mutex_top_waiter(&pi_state->pi_mutex);
> > +		if (!rt_waiter)
> > +			goto do_uncontended;
> 
> That ^ needs to drop wait_lock before the goto.

Ach, you noticed that one. Wrote a reply a few minutes after that one.

Sebastian