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[Luis Henriques <luis.henriques@xxxxxxxxxxxxx>]

** Changed in: linux (Ubuntu Precise)
       Status: Triaged => Fix Committed

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https://bugs.launchpad.net/bugs/1431280

Title:
  x86: mm/fault: Fix semaphore imbalance

Status in linux package in Ubuntu:
  Triaged
Status in linux source package in Precise:
  Fix Committed

Bug description:
  The qrt kernel_security are hanging with "task hung" errors/warnings
  on the console with Precise.  This seems to be due to an issue in the
  backport to the 3.2.67 stable kernel of commit:

  commit 33692f27597fcab536d7cbbcc8f52905133e4aa7
  Author: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
  Date:   Thu Jan 29 10:51:32 2015 -0800

      vm: add VM_FAULT_SIGSEGV handling support

  3.2.68 kernel fixes this issue with commit:

  commit 6749fd110bf44164782df9bba86c0327474446b9
  Author: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
  Date:   Wed Feb 25 00:02:28 2015 +0000

      x86: mm/fault: Fix semaphore imbalance
      
      When backporting commit 33692f27597f ('vm: add VM_FAULT_SIGSEGV
      handling support') I didn't notice that it depended on a recent change
      to the locking context of mm_fault_error() (commit 7fb08eca4527,
      'x86: mm: move mmap_sem unlock from mm_fault_error() to caller').
      That isn't easily applicable to 3.2, so instead make sure we drop
      mm->mmap_sem on the new branch of mm_fault_error().

  The ubuntu-qrt-apparmor are also hanging, possibly for the same
  reason.

  Including commit 6749fd110bf4 ("x86: mm/fault: Fix semaphore
  imbalance") in Precise seems to fix these issues.

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