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Do not mask edge-triggered interrupts to avoid losing them while masked, see Intel 82093AA I/O Advanced Programmable Interrupt Controller (IOAPIC) specification, section 3.4.2, "Interrupt Mask": "When this bit is 1, the interrupt signal is masked. Edge-sensitive interrupts signaled on a masked interrupt pin are ignored (i.e., not delivered or held pending)" Or to quote Linus Torvalds on the subject: "Now, edge-triggered interrupts are a _lot_ harder to mask, because the Intel APIC is an unbelievable piece of sh*t, and has the edge-detect logic _before_ the mask logic, so if a edge happens _while_ the device is masked, you'll never ever see the edge ever again (unmasking will not cause a new edge, so you simply lost the interrupt)." So when you "mask" an edge-triggered IRQ, you can't really mask it at all, because if you did that, you'd lose it forever if the IRQ comes in while you masked it. Instead, we're supposed to leave it active, and set a flag, and IF the IRQ comes in, we just remember it, and mask it at that point instead, and then on unmasking, we have to replay it by sending a self-IPI." [1] [1] - http://yarchive.net/comp/linux/edge_triggered_interrupts.html Ref #1448 |
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