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

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https://bugs.launchpad.net/bugs/1829563

Title:
  bcache: risk of data loss on I/O errors in backing or caching devices

Status in linux package in Ubuntu:
  Fix Committed
Status in linux source package in Bionic:
  Fix Committed
Status in linux source package in Cosmic:
  Won't Fix
Status in linux source package in Disco:
  In Progress
Status in linux source package in Eoan:
  Fix Committed

Bug description:
  [Impact]

   * The bcache code in Bionic lacks several fixes to handle
     I/O errors in both backing devices and caching devices.

   * Partial or permanent errors in backing or caching devices,
     specially in writeback mode, can lead to data loss and/or
     the application is not notified about failed I/O requests.

   * The bcache device might remain available for I/O requests
     even if backing device is offline, so writes are undefined.

  [Test Case]

   * Detailed test cases/steps for the behavior of many patches
     with code logic changes are provided in bug comments.

   * The patchset has been tested for regressions on each cache
     mode (writethrough, writeback, writearound, none) with the
     xfstests test suite (on ext4) and fio (sequential + random
     read-write).

  [Regression Potential]

   * The patchset is relatively large and touches several areas
     in bcache code, however, synthetic testing of the patches
     has been performed, and extensive regression/stress tests
     were run (as mentioned in Test Case section).

   * Many patches in the patchset are 'Fixes' patches to other
     patches, and no further 'Fixes' currently exist upstream.

  [Other Info]

   * Canonical Field Eng. deploys bcache+writeback extensively
     (e.g., BootStack, UA cloud, except rare all-flash cases).

  [Original Bug Description]

  This is a request for a backport of the following upstream patch from
  4.18:

  "bcache: stop bcache device when backing device is offline"
  
https://github.com/torvalds/linux/commit/0f0709e6bfc3ce4e8e1c0e8573490c45f76cfeee

  Field engineering uses bcache quite extensively and it would be good
  to have this in the GA/bionic kernel.

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