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[Andy Whitcroft <apw@xxxxxxxxxxxxx>]

Fix released in 4.2.0-27.32

** Changed in: linux (Ubuntu Wily)
       Status: Fix Committed => Fix Released

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https://bugs.launchpad.net/bugs/1526811

Title:
  SRU: walker list corruption while being intensively stressed

Status in Linux:
  Unknown
Status in linux package in Ubuntu:
  Fix Released
Status in linux source package in Wily:
  Fix Released
Status in linux source package in Xenial:
  Fix Released

Bug description:
  [SRU Justification][Wily]  + [Xenial]

  While stress testing with the stress-ng procfs stressor I hit a walker
  list bug.  This has been recently fixed by Herbert Xu in commit:

  The commit ba7c95ea3870fe7b847466d39a049ab6f156aa2c ("rhashtable: Fix
  sleeping inside RCU critical section in walk_stop") introduced a new
  spinlock for the walker list.  However, it did not convert all
  existing users of the list over to the new spin lock.  Some continued
  to use the old mutex for this purpose.  This obviously led to
  corruption of the list.

  [Fix]
  Clean upstream cherry pick, commit c6ff5268293ef98e48a99597e765ffc417e39fa5
  Will land in Xenial automatically (4.4)

  
  [Testcase]
  Run multiple instances of the attached code on a multicore system.  Alternatively, run stress-ng --procfs 0 on a multi-core system

  Fix will stop the above code corrupting the list and crashing.

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