On Sun, Sep 22, 2013 at 07:45:01AM +1000, Benjamin Herrenschmidt wrote: > On Sat, 2013-09-21 at 13:58 -0500, Frederic Weisbecker wrote: > > > Now certainly what needs to be fixed then is archs that don't have > > __ARCH_IRQ_EXIT_IRQS_DISABLED > > or archs that have any other significant opportunity to nest interrupt. > > Interesting. I notice we don't define it on powerpc
Yeah, x86 doesn't define it either. In fact few archs do. > but we don't enable > IRQs in do_IRQ either... our path is very similar to x86 in this regard, > the only thing that can cause them to become enabled would be if a > driver interrupt handler did local_irq_enable(). > > It used to be fairly common for drivers to do spin_unlock_irq() which > would unconditionally re-enable. Did we add WARNs or lockdep logic to > catch these nowadays ? Right there is a check in handle_irq_event_percpu() that warns if the handler exits with irqs enabled. And irq_exit() also warns when (__ARCH_IRQ_EXIT_IRQS_DISABLED && !irq_disabled()) > > > > - process context doing local_bh_enable, and a bh became pending > > > while it was disabled. See above: this needs a stack switch. Which > > > stack to use is open, again assuming that a hardirq coming in will > > > switch to yet another stack. > > > > Right. Now if we do like Thomas suggested, we can have a common irq > > stack that is big enough for hard and softirqs. After all there should > > never be more than two or three nesting irq contexts: > > hardirq->softirq->hardirq, softirq->hardirq, ... > > > > At least if we put aside the unsane archs that can nest irqs somehow. > > I really don't like the "larger" irq stack ... probably because I can't > make it work easily :-) See my previous comment about how we get to > thread_info on ppc. > > What I *can* do that would help I suppose would be to switch to the irq > stack before irq_enter/exit which would at least mean that softirq would > run from the top of the irq stack which is better than the current > situation. Yeah I think that doing this should solve the biggest part of the problem on ppc. You'll at least ensure that you have splitup stacks for tasks and softirq/irq stacks. > > I'm fact I'll whip up a quick fix see if that might be enough of a band > aid for RHEL7. > > Cheers, > Ben. > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/