Re: [PATCH,RFC] Add call_rcu_sched()

[Gautham R Shenoy]

On Tue, Apr 08, 2008 at 01:39:36AM -0700, Andrew Morton wrote:
> On Tue, 8 Apr 2008 13:40:48 +0530 Gautham R Shenoy <ego@xxxxxxxxxx> wrote:
> 
> > > > +			rdp = RCU_DATA_CPU(cpu);
> >                                                                <-- here ------\
> > > > +			spin_lock_irqsave(&rdp->lock, flags);                   |
> > > > +                                                                         |
> > > > +			/*                                                      |
> > > > +			 * We are running on this CPU irq-disabled, so no       |
> > > > +			 * CPU can go offline until we re-enable irqs.          |
> > >                                                                             |
> > > but, but, but.  The cpu at `cpu' could have gone offline just before we     |
> > > disabled local interrupts.                                                  |
> >                                                                               |
> > In that case the CPU_DEAD callback should have migrated the rcu-lists to      |
> > a cpu which is online.                                                        |
>                                                                                 |
> But local variable rdp might be pointing at the now-offlined CPU's data? -------/

Right. But then rdp wouldn't contain anything useful at this point.
So, we may only end up taking the rdp->lock, observe that there's nothing to do,
and move on.

Is there something else that I am missing?

-- 
Thanks and Regards
gautham
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/