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The following was observed by Kar Hin Ong with RT patchset: Backtrace: irq 19: nobody cared (try booting with the "irqpoll" option) CPU: 0 PID: 3329 Comm: irq/34-nipalk Tainted:4.14.87-rt49 #1 Hardware name: National Instruments NI PXIe-8880/NI PXIe-8880, BIOS 2.1.5f1 01/09/2020 Call Trace: <IRQ> ? dump_stack+0x46/0x5e ? __report_bad_irq+0x2e/0xb0 ? note_interrupt+0x242/0x290 ? nNIKAL100_memoryRead16+0x8/0x10 [nikal] ? handle_irq_event_percpu+0x55/0x70 ? handle_irq_event+0x4f/0x80 ? handle_fasteoi_irq+0x81/0x180 ? handle_irq+0x1c/0x30 ? do_IRQ+0x41/0xd0 ? common_interrupt+0x84/0x84 </IRQ> ... handlers: [<ffffffffb3297200>] irq_default_primary_handler threaded [<ffffffffb3669180>] usb_hcd_irq Disabling IRQ #19 The problem being that this device is triggering boot interrupts due to threaded interrupt handling and masking of the IO-APIC. These boot interrupts are then forwarded on to the legacy PCH's PIRQ lines where there is no handler present for the device. Whenever a PCI device fires interrupt (INTx) to Pin 20 of IOAPIC 2 (GSI 44), the kernel receives two interrupts: 1. Interrupt from Pin 20 of IOAPIC 2 -> Expected 2. Interrupt from Pin 19 of IOAPIC 1 -> UNEXPECTED Quirks for disabling boot interrupts (preferred) or rerouting the handler exist but do not address these Xeon chipsets' mechanism: https://lore.kernel.org/lkml/12131949181903-git-send-email-sassmann@suse.de/ Add a new mechanism via PCI CFG for those chipsets supporting CIPINTRC register's dis_intx_rout2ich bit. Link: https://lore.kernel.org/r/20200220192930.64820-2-sean.v.kelley@linux.intel.com Reported-by: Kar Hin Ong <kar.hin.ong@ni.com> Tested-by: Kar Hin Ong <kar.hin.ong@ni.com> Signed-off-by: Sean V Kelley <sean.v.kelley@linux.intel.com> Signed-off-by: Bjorn Helgaas <bhelgaas@google.com> Reviewed-by: Thomas Gleixner <tglx@linutronix.de> Cc: stable@vger.kernel.org
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.