[Bug 1942784] Re: makedumpfile falls back to cp on focal with 5.11 kernel

[Mauricio Faria de Oliveira]

Reviewed and uploaded to Focal. Thanks @joalif!

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https://bugs.launchpad.net/bugs/1942784

Title:
  makedumpfile falls back to cp on focal with 5.11 kernel

Status in makedumpfile package in Ubuntu:
  Fix Released
Status in makedumpfile source package in Focal:
  In Progress
Status in makedumpfile source package in Hirsute:
  Invalid

Bug description:
  [IMPACT]

  When running Focal with the hwe 5.11 kernel makedumpfile is not working as it should.
  Instead of compressing the dump makedumpfile falls back to cp.
  This can create problems on systems with very large RAM and result into exhausting all storage on the host.

  [FIX]

  This can be resolved with upstream commit f1197543d1c4 ([PATCH] Retrieve MAX_PHYSMEM_BITS from vmcoreinfo).
  The reason for falling back to cp is that without this patch makedumpfile calculates wrongly the memory layout.

  This happens after the kernel commit 1d50e5d0c505 ("crash_core, vmcoreinfo: Append 'MAX_PHYSMEM_BITS'to vmcoreinfo").
  With this commit applied, reading MAX_PHYSMEM_BITS from vmcoreinfo instead of inferring lead to correctly detecting the memory layout and creating the dump file properly.

  [TEST CASE]

  For testing a machine running focal with the 5.11 kernel is required.
  Then trigger a crash.
  On the console we can see that makedumpfile fails and `falls back to cp`.
  In /var/crash we can see that no dmesg file is created and instead of the dump file
  the uncompressed vmcoreinfo is created.

  [WHERE PROBLEMS COULD OCCUR]

  Any regression potential would involve the crash dump not being
  created after a crash in case kdump is configured.

  [OTHER]

  Only Focal with 5.11 kernel is affected.

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