** Changed in: linux (Ubuntu Bionic)
       Status: In Progress => Fix Committed

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https://bugs.launchpad.net/bugs/1765232

Title:
  Kernel 4.15.0-15 breaks Dell PowerEdge 12th Gen servers

Status in linux package in Ubuntu:
  Fix Committed
Status in linux source package in Bionic:
  Fix Committed

Bug description:
  SRU Justification

  Impact: Since 4.15.0-15 some machines have been failing to boot due to
  IO hangs. This is caused by patches applied for LP #1759723, which
  assigned managed interrupt vectors and reply queues for all possible
  CPUs, not just present CPUs. Some drivers were not prepared to cope
  with this and end up selecting reply queues not mapped to an online
  CPU, causing IO hangs during boot.

  Fix: There are driver fixes available upstream, but there are 8-ish
  patches in total and we're extremely close to release, so the safer
  bet it to just revert the patches for LP #1759723. We can consider
  reintroducing them with required fixes at a later time.

  Regression Potential: This is obviously going to reintroduce the
  problem the patches were intended to fix. These are less serious than
  the problems which the patches introduced, and IBM has given their
  okay to revert them as well.

  Test Case: Verified to fix affected hardware on LP #1765232.

  ---

  For Ubuntu 18.04 amd64 server, I updated the kernel from 4.15.0-13 to
  4.15.0-15. The system hangs at boot up now. Rolling back to the old
  kernel everything works as expected. It appears to hang while trying
  to enumerate an SD card device, which isn't even installed. I have
  tried this on a Dell R620 and R820 and both have the exact same
  problem. I even downloaded a new installer iso from the daily builds
  to reinstall the OS and the installer hangs too now.

  Support for Dell PowerEdge 12th gen servers appears to be broken with
  kernel 4.15.0-15.

  https://imgur.com/VT9zd0w
  https://imgur.com/4BQPCXo

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