linux-kernel - Re: [PATCH 04/16] rcu: rcutiny: Prevent RCU stall

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Date:	Mon, 18 Feb 2013 10:02:01 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	paulmck@...ux.vnet.ibm.com
Cc:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org,
	Carsten Emde <C.Emde@...dl.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 04/16] rcu: rcutiny: Prevent RCU stall

On Sat, 2013-02-16 at 12:59 -0800, Paul E. McKenney wrote:
>  
> > diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h
> > index 2b0484a..bac1906 100644
> > --- a/kernel/rcutiny_plugin.h
> > +++ b/kernel/rcutiny_plugin.h
> > @@ -552,7 +552,7 @@ static void rcu_read_unlock_special(struct task_struct *t)
> >  		rcu_preempt_cpu_qs();
> > 
> >  	/* Hardware IRQ handlers cannot block. */
> > -	if (in_irq()) {
> > +	if (preempt_count() & (HARDIRQ_MASK | SOFTIRQ_OFFSET)) {
> 
> For whatever it is worth, in mainline this is:
> 
> 	if (in_irq() || in_serving_softirq()) {
> 
> The definition of in_serving_softirq() is a bit different:
> 
> #define in_serving_softirq()    (softirq_count() & SOFTIRQ_OFFSET)
> 
> This might be due to differences between mainline and -rt, but thought
> it worth calling attention to.
> 

Right, and we should avoid open coding HARDIRQ_MASK and SOFTIRQ_OFFSET. 
And note, -rt is slowly creeping into mainline. It's better to have
things like this nicely tidied up.

-- Steve


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