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30e748a507
This matters to any sort of device that is wired to one of the CPU interrupt pins on an SMP system. Typically the scenario is most easily triggered with the count/compare timer interrupt where the same interrupt number and thus irq_desc is used on each processor. CPU A CPU B do_IRQ() generic_handle_irq() handle_level_irq() spin_lock(desc_lock) set IRQ_INPROGRESS spin_unlock(desc_lock) do_IRQ() generic_handle_irq() handle_level_irq() spin_lock(desc_lock) IRQ_INPROGRESS set => bail out spin_lock(desc_lock) clear IRQ_INPROGRESS spin_unlock(desc_lock) In case of the cp0 compare interrupt this means the interrupt will be acked and not handled or re-armed on CPU b, so there won't be any timer interrupt until the count register wraps around. With kernels 2.6.20 ... 2.6.23 we usually were lucky that things were just working right on VSMP because the count registers are synchronized on bootup so it takes something that disables interrupts for a long time on one processor to trigger this one. For scenarios where an interrupt is multicasted or broadcasted over several CPUs the existing code was safe and the fix will break it. There is no way to know in the interrupt controller code because it is abstracted from the platform code. I think we do not have such a setup currently, so this should be ok. Signed-off-by: Ralf Baechle <ralf@linux-mips.org> |
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