On Mon, Oct 26 2020 at 12:06, Guilherme Piccoli wrote: > On Sun, Oct 25, 2020 at 8:12 AM Pingfan Liu <kernelfans@xxxxxxxxx> wrote: > > Some time ago (2 years) we faced a similar issue in x86-64, a hard to > debug problem in kdump, that eventually was narrowed to a buggy NIC FW > flooding IRQs in kdump kernel, and no messages showed (although kernel > changed a lot since that time, today we might have better IRQ > handling/warning). We tried an early-boot fix, by disabling MSIs (as > per PCI spec) early in x86 boot, but it wasn't accepted - Bjorn asked > pertinent questions that I couldn't respond (I lost the reproducer) > [0]. ... > [0] lore.kernel.org/linux-pci/20181018183721.27467-1-gpiccoli@xxxxxxxxxxxxx With that broken firmware the NIC continued to send MSI messages to the vector/CPU which was assigned to it before the crash. But the crash kernel has no interrupt descriptor for this vector installed. So Liu's patches wont print anything simply because the interrupt core cannot detect it. To answer Bjorns still open question about when the point X is: https://lore.kernel.org/linux-pci/20181023170343.GA4587@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/ It gets flooded right at the point where the crash kernel enables interrupts in start_kernel(). At that point there is no device driver and no interupt requested. All you can see on the console for this is "common_interrupt: $VECTOR.$CPU No irq handler for vector" And contrary to Liu's patches which try to disable a requested interrupt if too many of them arrive, the kernel cannot do anything because there is nothing to disable in your case. That's why you needed to do the MSI disable magic in the early PCI quirks which run before interrupts get enabled. Also Liu's patch only works if: 1) CONFIG_IRQ_TIME_ACCOUNTING is enabled 2) the runaway interrupt has been requested by the relevant driver in the dump kernel. Especially #1 is not a sensible restriction. Thanks, tglx _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
