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

[Brian Murray]

Hello Ian, or anyone else affected,

Accepted lttng-modules into eoan-proposed. The package will build now
and be available at https://launchpad.net/ubuntu/+source/lttng-
modules/2.10.8-1ubuntu2.1 in a few hours, and then in the -proposed
repository.

Please help us by testing this new package.  See
https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how
to enable and use -proposed.  Your feedback will aid us getting this
update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug,
mentioning the version of the package you tested, what testing has been
performed on the package and change the tag from verification-needed-
eoan to verification-done-eoan. If it does not fix the bug for you,
please add a comment stating that, and change the tag to verification-
failed-eoan. In either case, without details of your testing we will not
be able to proceed.

Further information regarding the verification process can be found at
https://wiki.ubuntu.com/QATeam/PerformingSRUVerification .  Thank you in
advance for helping!

N.B. The updated package will be released to -updates after the bug(s)
fixed by this package have been verified and the package has been in
-proposed for a minimum of 7 days.

** Changed in: lttng-modules (Ubuntu Eoan)
       Status: In Progress => Fix Committed

** Tags added: verification-needed-eoan

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https://bugs.launchpad.net/bugs/1874521

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:
  Fix Committed
Status in lttng-modules source package in Focal:
  Fix Committed

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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