[Bug 1797990] Re: kdump fail due to an IRQ storm

** Description changed:

[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).
+  * 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.
+
+ * $ 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@canonical.com/

   [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@canonical.com/

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

[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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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:
Confirmed
Status in linux source package in Xenial:
Confirmed
Status in linux source package in Bionic:
Confirmed
Status in linux source package in Cosmic:
Confirmed

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.

* $ 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@canonical.com/

   [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@canonical.com/

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

[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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