Our IRQ storm detection works when an interrupt handler returns IRQ_NONE for thousands of consecutive interrupts in a second. It doesn't hurt to occasionally return IRQ_NONE when the interrupt is actually genuine.
Drivers should only be returning IRQ_HANDLED if they have actually *done* something to stop an interrupt from happening — it doesn't just mean "this really *was* my device". Signed-off-by: David Woodhouse <david.woodho...@intel.com> --- See recent discussion about the 8139cp Ethernet driver¹. It developed (OK, I introduced) a bug where it would re-enable the RX IRQ when handling a TX timeout and resetting the hardware. This leads to an IRQ storm with cp_interrupt() *not* doing anything about the RX IRQ, because NAPI was already scheduled. And then returning IRQ_HANDLED anyway. And complete death of the machine. Our IRQ storm detection should handle that kind of thing — it's designed to catch both hardware *and* software screwups. But because of the cp_interrupt() return value, it didn't. I tried to fix cp_interrupt(), and submitted a patch which made the failure mode much saner — the offending IRQ got disabled and the machine continued happily, with the network even *working* in polling mode. It met with resistance. To overcome that resistance, we should clearly document the expectation that device drivers should return IRQ_NONE in that kind of case. Let's start by at least fixing the *wrong* text in irqreturn.h, which says that IRQ_NONE means "not my device"... ¹ http://www.spinics.net/lists/netdev/msg343991.html http://www.spinics.net/lists/netdev/msg343995.html http://www.spinics.net/lists/netdev/msg344265.html diff --git a/include/linux/irqreturn.h b/include/linux/irqreturn.h index e374e36..eb1bdcf 100644 --- a/include/linux/irqreturn.h +++ b/include/linux/irqreturn.h @@ -3,7 +3,7 @@ /** * enum irqreturn - * @IRQ_NONE interrupt was not from this device + * @IRQ_NONE interrupt was not from this device or was not handled * @IRQ_HANDLED interrupt was handled by this device * @IRQ_WAKE_THREAD handler requests to wake the handler thread */ -- David Woodhouse Open Source Technology Centre david.woodho...@intel.com Intel Corporation
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