Re: [PATCH v2] rtmutex: take the waiter lock with irqs off

From: Peter Zijlstra <peterz@infradead.org>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	Thomas Gleixner <tglx@linutronix.de>,
	Mike Galbraith <bitbucket@online.de>,
	LKML <linux-kernel@vger.kernel.org>,
	RT <linux-rt-users@vger.kernel.org>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: Re: [PATCH v2] rtmutex: take the waiter lock with irqs off
Date: Tue, 19 Nov 2013 09:30:15 +0100	[thread overview]
Message-ID: <20131119083015.GF10022@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20131118235956.GA1810@localhost.localdomain>

On Tue, Nov 19, 2013 at 12:59:59AM +0100, Frederic Weisbecker wrote:
> On Mon, Nov 18, 2013 at 03:10:21PM +0100, Peter Zijlstra wrote:
> > --- a/kernel/softirq.c
> > +++ b/kernel/softirq.c
> > @@ -746,13 +746,23 @@ void irq_exit(void)
> >  #endif
> >  
> >  	account_irq_exit_time(current);
> > -	trace_hardirq_exit();
> >  	sub_preempt_count(HARDIRQ_OFFSET);
> > -	if (!in_interrupt() && local_softirq_pending())
> > +	if (!in_interrupt() && local_softirq_pending()) {
> > +		/*
> > +		 * Temp. disable hardirq context so as not to confuse lockdep;
> > +		 * otherwise it might think we're running softirq handler from
> > +		 * hardirq context.
> > +		 *
> > +		 * Should probably sort this someplace else..
> > +		 */
> > +		trace_hardirq_exit();
> >  		invoke_softirq();
> > +		trace_hardirq_enter();
> > +	}
> >  
> >  	tick_irq_exit();
> >  	rcu_irq_exit();
> > +	trace_hardirq_exit();
> 
> Looks like a change we really want!

Yeah, let me stare at the softirq mess again to see if there's anything
better/prettier we can do.