group.of.nepali.translators team mailing list archive

["Guilherme G. Piccoli" <1797990@xxxxxxxxxxxxxxxxxx>]

Thanks Maurício for submitting the patches and taking care of the bug
while I was out.

I've verified all the 3 releases (in fact, I've also verified Trusty HWE) with a similar
test as used by Maurício, "dmesg -t | sort" and the kernels are running fine.
During kdump, with the "pci=clearmsi" option, we can see the message:

"Clearing MSI/MSI-X enable bits early in boot (quirk)"
which shows that the quirk is working.

I'll attach the logs for documentation purposes.
Cheers,


Guilherme

** Changed in: linux (Ubuntu Trusty)
       Status: Confirmed => Won't Fix

** Tags removed: verification-needed-bionic verification-needed-cosmic verification-needed-xenial
** Tags added: verification-done-bionic verification-done-cosmic verification-done-xenial

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https://bugs.launchpad.net/bugs/1797990

Title:
  kdump fail due to an IRQ storm

Status in linux package in Ubuntu:
  Confirmed
Status in linux source package in Trusty:
  Won't Fix
Status in linux source package in Xenial:
  Fix Committed
Status in linux source package in Bionic:
  Fix Committed
Status in linux source package in Cosmic:
  Fix Committed

Bug description:
  [Impact]

   * A kexec/crash kernel might get stuck and fail to boot
     (for crash kernel, kdump fails to collect a crashdump)
     if a PCI device is buggy/stuck/looping and triggers a
     continuous flood of MSI(X) interrupts (that the kernel
     does not yet know about).

   * This fix allowed to obtain crashdumps when debugging a
     heavy-load scenario, in which a (heavy-loaded) network
     adapter wouldn't stop triggering MSI-X interrupts ever
     after panic()->kdump kicked in.

   * This fix disables MSI(X) in all PCI devices on early
     boot (this is OK as it's (re-)enabled normally later)
     with a kernel cmdline parameter (disabled by default).

  [Test Case]

   * A synthetic test-case is not yet available, however,
     this particular system/workload triggered the problem
     consistently, and it was used for development/testing.

   * We'll update this bug once a synthetic test-case is
     available; we're working on patching QEMU for this.

   * $ cat /proc/cmdline
     <...> pci=clearmsi

     $ dmesg | grep 'Clearing MSI'
     [    0.000000] Clearing MSI/MSI-X enable bits early in boot (quirk)

   * The comparison of 'dmesg -t | sort' has been reviewed
     between option disabled/enabled on boot & kexec modes,
     and only expected differences found (MHz, PIDs, MIPS).

  [Regression Potential]

   * The potential area for regressions is early boot,
     particularly effects of applying quirks during PCI
     bus scan, which is changed/broader w/ these patches.

   * However, all quirks are applied based on PCI ID
     matching, so would only apply if actually targeting
     a new device.

   * Moreover, the new quirk is only applied based on
     a kernel cmdline parameter that is disabled by
     default, which constraints even more when this
     is actually in effect.

  [Other Info]

   * The patch series is still under review/discussion
     upstream, but it's relatively important for Ubuntu
     users at this point, and after internal discussions
     we decided to submit it for SRU.

   * These are links to the linux-pci archive with the
     patches [1, 2, 3]

     [1] [PATCH 1/3] x86/quirks: Scan all busses for early PCI quirks
         https://lore.kernel.org/linux-pci/20181018183721.27467-1-gpiccoli@xxxxxxxxxxxxx/

     [2] [PATCH 2/3] x86/PCI: Export find_cap() to be used in early PCI code
         https://lore.kernel.org/linux-pci/20181018183721.27467-2-gpiccoli@xxxxxxxxxxxxx/

     [3] [PATCH 3/3] x86/quirks: Add parameter to clear MSIs early on boot
         https://lore.kernel.org/linux-pci/20181018183721.27467-3-gpiccoli@xxxxxxxxxxxxx/

  [Original Description]

  We have reports of a kdump failure in Ubuntu (in x86 machine) that was
  narrowed down to a MSI irq storm coming from a PCI network device.

  The bug manifests as a lack of progress in the boot process of the
  kdump kernel, and a storm of kernel messages like:

  [...]
  [  342.265294] do_IRQ: 0.155 No irq handler for vector
  [  342.266916] do_IRQ: 0.155 No irq handler for vector
  [  347.258422] do_IRQ: 14053260 callbacks suppressed
  [...]

  The root cause of the issue is that the kdump kernel kexec process
  does not ensure PCI devices are reset and/or MSI capabilities are
  disabled, so a PCI device could produce a huge amount of PCI irqs
  which would take all the processing time for the CPU (specially since
  we restrict the kdump kernel to use one single CPU only).

  This was tested using upstream kernel version 4.18, and the problem reproduces.
  In the specific test scenario, the PCI NIC was an "Intel 82599ES 10-Gigabit [8086:10fb]" that was used in SR-IOV PCI passthrough mode (vfio_pci), under high load on the guest.

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