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

Steven Rostedt
2013-02-18T15:02:01Z

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