[Bug 1874521] Re: lttng-modules 2.10.8-1ubuntu2~18.04.1 ADT test failure with linux-kvm 4.15.0-1059.60

[Christian Ehrhardt ]

Please update debdiffs a bit:
1. where you link the commit please use proper origin tags
  Origin: backport, <todo-URL-to-git>
  # OTHERWISE
  Origin: upstream, <todo-URL-to-git>

2. your version numbers are incorrect for SRUs
+lttng-modules (2.11.2-1ubuntu1) focal; urgency=medium
needs to be 2.11.2-1ubuntu0.1

+lttng-modules (2.10.8-1ubuntu3) eoan; urgency=medium
needs to be 2.10.8-1ubuntu2.1

+lttng-modules (2.10.8-1ubuntu3~18.04.1) bionic; urgency=medium
needs to be 2.10.8-1ubuntu2~18.04.2

xenial is correct

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Title:
  lttng-modules 2.10.8-1ubuntu2~18.04.1 ADT test failure with linux-kvm
  4.15.0-1059.60

Status in lttng-modules package in Ubuntu:
  Won't Fix
Status in lttng-modules source package in Xenial:
  In Progress
Status in lttng-modules source package in Bionic:
  In Progress
Status in lttng-modules source package in Eoan:
  In Progress
Status in lttng-modules source package in Focal:
  In Progress

Bug description:
  Testing failed on:
      amd64: https://objectstorage.prodstack4-5.canonical.com/v1/AUTH_77e2ada1e7a84929a74ba3b87153c0ac/autopkgtest-bionic/bionic/amd64/l/lttng-modules/20200423_185643_adec8@/log.gz

  [SRU Justification]

  == Impact ==

  In linux 5.6 upstream replaced vmalloc_sync_all() by
  vmalloc_sync_mappings() and vmalloc_sync_unmappings(). Lttng uses
  vmalloc_sync_all() from a wrapper to prevent recursive page faults.
  The call is either made directly in the code or, if kallsyms is
  available, by looking up its address and then jumping indirectly.

  Recent stable updates backported that change into 4.4, 4.15, 5.3, and
  5.4. This affects lttng-modules. Either the build fails completely (if
  kallsyms is not enabled). Or there will be warnings at runtime:

    LTTng: vmalloc_sync_all symbol lookup failed.
    Page fault handler and NMI tracing might trigger faults.

  == Fix ==

  Backporting 4 patches from upstream lttng fixes the issue for 4.4 and
  5.4 (as those allow matching against linux kernel version). For 4.15
  and 5.3 and additional patch adds Ubuntu specific version ranges.

  Note, that this last patch also adds a range for 5.0 which was Disco.
  This should not hurt and also indirectly is needed for some backport
  kernels in 18.04/Bionic. But I want to try keeping the patches as
  similar as possible across releases.

  == Testcase ==

  Installation of lttng-modules-dkms, depending on kernel configuration either the build will fail or loading lttng-test (or checking dmesg after reboot) will show warnings.
  With the changes applied the build succeeds in all cases and no warnings appear.

  == Regression Potential ==

  Low, without the new function name present, everything would be
  unchanged and once the change is there, functionality already is
  regressed.

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