linux-kernel - Re: [PATCH 3/3] rtmutex: remove unnecessary adjust prio

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Date:   Wed, 12 Jul 2017 10:14:49 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Alex Shi <alex.shi@...aro.org>
Cc:     peterz@...radead.org, mingo@...hat.com, corbet@....net,
        "open list:LOCKING PRIMITIVES" <linux-kernel@...r.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        Sebastian Siewior <bigeasy@...utronix.de>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Juri Lelli <juri.lelli@....com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 3/3] rtmutex: remove unnecessary adjust prio

On Tue, 11 Jul 2017 22:39:24 +0800
Alex Shi <alex.shi@...aro.org> wrote:

> Any comments for this little change? It's passed on 0day testing.

I think the problem was that this was a third patch after two
documentation patches. Where, people put documentation review at the
bottom of their priority list.

This should have been sent as separate patch on its own.

> 
> Thanks
> Alex
> 
> On 07/07/2017 10:52 AM, Alex Shi wrote:
> > We don't need to adjust prio before new pi_waiter adding. The prio
> > only need update after pi_waiter change or task priority change.
> > 
> > Signed-off-by: Alex Shi <alex.shi@...aro.org>
> > Cc: Steven Rostedt <rostedt@...dmis.org>
> > Cc: Sebastian Siewior <bigeasy@...utronix.de>
> > Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
> > Cc: Juri Lelli <juri.lelli@....com>
> > Cc: Thomas Gleixner <tglx@...utronix.de>
> > To: linux-kernel@...r.kernel.org
> > To: Ingo Molnar <mingo@...hat.com>
> > To: Peter Zijlstra <peterz@...radead.org>
> > ---
> >  kernel/locking/rtmutex.c | 1 -
> >  1 file changed, 1 deletion(-)
> > 
> > diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
> > index 28cd09e..d1fe41f 100644
> > --- a/kernel/locking/rtmutex.c
> > +++ b/kernel/locking/rtmutex.c
> > @@ -963,7 +963,6 @@ static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
> >  		return -EDEADLK;
> >  
> >  	raw_spin_lock(&task->pi_lock);
> > -	rt_mutex_adjust_prio(task);

Interesting, I did some git mining and this was added with the original
entry of the rtmutex.c (23f78d4a0). Looking at even that version, I
don't see the purpose of adjusting the task prio here. It is done
before anything changes in the task.

Reviewed-by: Steven Rostedt (VMware) <rostedt@...dmis.org>

-- Steve


> >  	waiter->task = task;
> >  	waiter->lock = lock;
> >  	waiter->prio = task->prio;
> >