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[Po-Hsu Lin <po-hsu.lin@xxxxxxxxxxxxx>]

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

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https://bugs.launchpad.net/bugs/1793451

Title:
  mlock203 test in ubuntu_ltp_syscalls failed with Xenial kernel

Status in ubuntu-kernel-tests:
  Fix Released
Status in linux package in Ubuntu:
  Fix Released
Status in linux source package in Xenial:
  Fix Released

Bug description:
  == Justification ==
  When one vma was with flag VM_LOCKED|VM_LOCKONFAULT (by invoking
  mlock2(,MLOCK_ONFAULT)), it can again be populated with mlock() with
  VM_LOCKED flag only.

  There is a hole in mlock_fixup() which increase mm->locked_vm twice even
  the two operations are on the same vma and both with VM_LOCKED flags.

  The issue can be reproduced by following code:

    mlock2(p, 1024 * 64, MLOCK_ONFAULT); //VM_LOCKED|VM_LOCKONFAULT
    mlock(p, 1024 * 64);  //VM_LOCKED

  Then check the increase VmLck field in /proc/pid/status(to 128k).

  When vma is set with different vm_flags, and the new vm_flags is with
  VM_LOCKED, it is not necessarily be a "new locked" vma.

  There is a dedicated reproducer, the "mlock203" test in
  ubuntu_ltp_syscalls, you can see the failure for all the Ubuntu 4.4
  kernel:

   <<<test_start>>>
   tag=mlock203 stime=1537369891
   cmdline="mlock203"
   contacts=""
   analysis=exit
   <<<test_output>>>
   tst_test.c:1063: INFO: Timeout per run is 0h 05m 00s
   mlock203.c:63: FAIL: Locking one memory again increased VmLck

   Summary:
   passed   0
   failed   1
   skipped  0
   warnings 0

  == Fix ==
  b155b4fd (mm: mlock: avoid increase mm->locked_vm on mlock() when already mlock2(,MLOCK_ONFAULT))

  A test kernel for Xenial / Xenial-KVM could be found here:
  http://people.canonical.com/~phlin/kernel/lp-1793451-mlock203/

  == Regression Potential ==
  Low, this patch prevents mm->locked_vm from increment just by adding an extra check to see if the old vm_flags is already VM_LOCKED.

  == Test Case ==
  Run the mlock203 test in ubuntu_ltp_syscalls test suite. And it will pass with the patched kernel.

  ProblemType: Bug
  DistroRelease: Ubuntu 16.04
  Package: linux-image-4.4.0-1068-aws 4.4.0-1068.78
  ProcVersionSignature: User Name 4.4.0-1068.78-aws 4.4.144
  Uname: Linux 4.4.0-1068-aws x86_64
  ApportVersion: 2.20.1-0ubuntu2.18
  Architecture: amd64
  Date: Thu Sep 20 06:44:13 2018
  Ec2AMI: ami-0e32ec5bc225539f5
  Ec2AMIManifest: (unknown)
  Ec2AvailabilityZone: us-west-2b
  Ec2InstanceType: c3.large
  Ec2Kernel: unavailable
  Ec2Ramdisk: unavailable
  SourcePackage: linux-aws
  UpgradeStatus: No upgrade log present (probably fresh install)

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