On Thu, 24 Jul 2008 08:17:38 +1000 Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx> wrote: > > > The root cause of this bug lies in the fact that the XICS interrupt controller > > uses a radix tree for its reverse irq mapping and that we cannot allocate the tree > > nodes (even GFP_ATOMIC) with preemption disabled. > > Is that yet another caes of -rt changing some basic kernel semantics ? Ahem, not really new: http://lkml.org/lkml/2007/11/12/211 > > > In fact, we have 2 nested preemption disabling when we want to allocate > > a new node: > > > > - setup_irq() does a spin_lock_irqsave() before calling xics_startup() which > > then calls irq_radix_revmap() to insert a new node in the tree > > > > - irq_radix_revmap() also does a spin_lock_irqsave() (in irq_radix_wrlock()) > > before the radix_tree_insert() > > > > The first patch moves the call to irq_radix_revmap() from xics_startup() out to > > xics_host_map_direct() and xics_host_map_lpar() which are called with preemption > > enabled. > > I suppose that would work. It should indeed. Instead of inserting the new mapping at request_irq() time, we do it a bit before at create_irq_mapping time. > > > The second patch is a little more involved in that it takes advantage of > > the concurrent radix tree to simplify the locking requirements and allows > > to allocate a new node outside a preemption disabled section. > > > > I just hope I've correctly understood the concurrent radix trees semantic > > and got the (absence of) locking right. > > Hrm, that will need some scrutinity. Yep, that will need a few more pair of eyes along with brains behind those ;-) Thanks, Sebastien. > > Thanks for looking at this. > > Cheers, > Ben. > > > -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
