[Bug 1681909] Re: kdump is not captured in remote host when kdump over ssh is configured

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Title:
  kdump is not captured in remote host when kdump over ssh is configured

Status in The Ubuntu-power-systems project:
  In Progress
Status in makedumpfile package in Ubuntu:
  In Progress
Status in makedumpfile source package in Xenial:
  In Progress
Status in makedumpfile source package in Bionic:
  In Progress
Status in makedumpfile source package in Cosmic:
  In Progress
Status in makedumpfile source package in Disco:
  In Progress
Status in makedumpfile source package in Eoan:
  In Progress

Bug description:
  [Impact]

  * Kdump over network (like NFS mount or SSH dump) relies on network-
  online target from systemd. Even so, there are some NICs that report
  "Link Up" state but aren't ready to transmit packets. This is a
  generally bad behavior that is credited probably to NIC firmware
  delays, usually not fixable from drivers. Some adapters known to act
  like this are bnx2x, tg3 and ixgbe.

  * Kdump is a mechanism that may be a last resort to debug complex/hard
  to reproduce issues, so it's interesting to increase its reliability /
  resilience. We then propose here a solution/quirk to this issue on
  network dump by adding a retry/delay mechanism; if it's a network
  dump, kdump will retry some times and sleep between the attempts in
  order to exclude the case of NICs that aren't ready yet but will soon
  be able to transmit packets.

  * Although first reported by IBM in PowerPC arch, the scope for this
  issue is the NIC, and it was later reported in x86 arch too.

  [Test case]

  Usually it's difficult to naturally reproduce this issue in a deterministic way, but we have an artificial test case on comment #24 of this LP.
  Also, we have a report from this bug in which the user managed to reproduce the problem consistently - it's fixed after testing our solution.

  [Regression potential]

  There's not a clear regression potential here since it's just a retry/delay mechanism. Some potential problems may come from bad coding in the script.
  The delay between attempts is only 3 sec per iteration, so it shouldn't block the kdump progress for a high amount of time at once.

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