linux-kernel - Re: [PATCH RT] locking/rtmutex: don't drop the wait

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Message-ID: <20170921164302.igwgum5pou66pmj3@linutronix.de>
Date:   Thu, 21 Sep 2017 18:43:02 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>, tglx@...utronix.de
Subject: Re: [PATCH RT] locking/rtmutex: don't drop the wait_lock twice

On 2017-09-21 12:31:05 [-0400], Steven Rostedt wrote:
> > diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
> > index f03876322d4a..79f49d73e4d0 100644
> > --- a/kernel/locking/rtmutex.c
> > +++ b/kernel/locking/rtmutex.c
> > @@ -2281,7 +2281,6 @@ int __rt_mutex_start_proxy_lock(struct rt_mutex *lock,
> >  	raw_spin_lock(&task->pi_lock);
> >  	if (task->pi_blocked_on) {
> >  		raw_spin_unlock(&task->pi_lock);
> > -		raw_spin_unlock_irq(&lock->wait_lock);
> 
> Hmm, before this patch, irqs are enabled when returning with -EAGAIN.
> But now they are not. Should that be:
> 
> 		raw_spin_unlock_irq(&taks->pi_lock);
> 
> or is there something that changes this?

There is something else. Before that futex rework there was just
rt_mutex_start_proxy_lock() and it did lock & unlock of ->wait_lock.
This no longer the case after the rework. So now the caller does this.

> -- Steve

Sebastian