lttng team mailing list archive

[Stefan Bader <stefan.bader@xxxxxxxxxxxxx>]

Deferring the fix for Groovy. This is being worked on in parallel and
will include additional changes to allow compiling against a 5.7 kernel.

** Changed in: lttng-modules (Ubuntu)
       Status: Triaged => Won't Fix

** Description changed:

  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.
+   LTTng: vmalloc_sync_all symbol lookup failed.
+   Page fault handler and NMI tracing might trigger faults.
  
  == Fix ==
  
- The proposed fix would check the kernel header for vmalloc_sync_mappings
- and if available, replace strings and calls with the correct function
- name.
+ 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.
  
  == Testcase ==
  
- Installation of lttng-modules-dkms, depending on kernel configuration
- either the build will fail or loading lttng modules (tried lttng-probe-
- rcu manually but on each reboot all modules seem to get loaded) will
- produce above warning messages.
+ 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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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:
  Triaged
Status in lttng-modules source package in Bionic:
  Triaged
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.

  == 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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