Messages in this thread | | | Subject | Re: [RFC GIT PULL] softirq: Consolidation and stack overrun fix | From | Benjamin Herrenschmidt <> | Date | Sun, 22 Sep 2013 07:45:01 +1000 |
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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 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 ?
> > - 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.
I'm fact I'll whip up a quick fix see if that might be enough of a band aid for RHEL7.
Cheers, Ben.
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