Re: [RFC][PATCH 5/8] rtmutex: Clean up

From: Juri Lelli <juri.lelli@arm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: mingo@kernel.org, tglx@linutronix.de, rostedt@goodmis.org,
	xlpang@redhat.com, linux-kernel@vger.kernel.org,
	mathieu.desnoyers@efficios.com, jdesfossez@efficios.com,
	bristot@redhat.com
Subject: Re: [RFC][PATCH 5/8] rtmutex: Clean up
Date: Tue, 14 Jun 2016 13:41:14 +0100	[thread overview]
Message-ID: <20160614124114.GI5981@e106622-lin> (raw)
In-Reply-To: <20160614123253.GH30921@twins.programming.kicks-ass.net>

On 14/06/16 14:32, Peter Zijlstra wrote:
> On Tue, Jun 14, 2016 at 01:08:13PM +0100, Juri Lelli wrote:
> > > +	postunlock = rt_mutex_futex_unlock(&pi_state->pi_mutex, &wake_q);
> > >  
> > >  	/*
> > >  	 * First unlock HB so the waiter does not spin on it once he got woken
> > > +	 * up. Then wakeup the waiter by calling rt_mutex_postunlock(). Priority
> > > +	 * is already adjusted and preemption is disabled to avoid inversion.
> > >  	 */
> > >  	spin_unlock(&hb->lock);
> > >  
> > > +	if (postunlock)
> > > +		rt_mutex_postunlock(&wake_q);
> > 
> > I'm most probably missing something, but don't we still need to call
> > wake_up_q() even when postunlock is false? IIUC, we were always doing
> > that, rt_mutex_postunlock(), before this change (only calling
> > preempt_enable() was conditional).
> 
> Note that rt_mutex_slowunlock() only uses wake_q on the true path. When
> it returns false, it will not have placed a task to wake up.
> 

Right. But, I thought we were still ending up calling wake_up_q before
this change. Which however looked fine, as it won't do anything if no
task is queued I guess. So, no problem before and no problem now I'd
say. :-)