[Bug 1398859] Re: [regression] unmounting NTFS causes mount.ntfs process to get stuck in eternal kernel deep sleep

[Martin Pitt]

- ntfs-3g itself did not change since utopic.
- The  hang happens with utopic's 3.16.0-23-generic and the previous 3.16.0-24-generic kernel too, so not a kernel regression.
- The hang happens with libc{6,-bin} 2.19-10ubuntu2, so not a glibc regression
- The hang happens with systemd+udev 215-5ubuntu2 (which we had from Nov 03 on), so not an udev regression either.

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Title:
  [regression] unmounting NTFS causes mount.ntfs process to get stuck in
  eternal kernel deep sleep

Status in ntfs-3g package in Ubuntu:
  New

Bug description:
  Since Mid-November the udisks2 test (https://jenkins.qa.ubuntu.com/job
  /vivid-adt-udisks2/? shows it happened between Nov 13 and 19) exhibits
  a regression with NTFS: Unmounting causes the ntfs-3g process to go
  into kernel deep sleep and umount hangs forever.

  This can be reproduced with

    sudo apt install ntfs-3g
    sudo modprobe scsi_debug
    # check dmesg which drive this created; e. g. /dev/sda
    sudo mkntfs -F /dev/sda
    sudo mount /dev/sda /mnt

  Now you have a process which is happy:
  root     12821  0.0  0.0  15272  1948 ?        Ss   15:49   0:00 /sbin/mount.ntfs /dev/sda /mnt -o rw

  You can work with /mnt, edit files, etc. But now unmount:

    sudo umount /mnt

  This never returns, and  the process goes into uninterruptible kernel
  sleep ("D"):

  root     12928  0.0  0.0  15272  1948 ?        Ds   15:55   0:00
  /sbin/mount.ntfs /dev/sda /mnt -o rw

  The strace for the umount until the hang is

  ubuntu at autopkgtest:~$ sudo strace -vvtts1024 -p 12928
  Process 12928 attached
  15:56:17.938299 read(4, "0\0\0\0\2\0\0\0\2\0\0\0\0\0\0\0\1\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\1\0\0\0\0\0\0\0", 135168) = 48
  15:56:22.338931 read(4, "(\0\0\0&\0\0\0\3\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0", 135168) = 40
  15:56:22.339637 sendto(5, "<29>Dec  3 15:56:22 ntfs-3g[12928]: Unmounting /dev/sda ()\n", 59, MSG_NOSIGNAL, NULL, 0) = 59
  15:56:22.340509 fsync(3)                = 0
  15:56:22.341188 fcntl(3, F_SETLK, {type=F_UNLCK, whence=SEEK_SET, start=0, len=0}) = 0
  15:56:22.341759 close(3

  ProblemType: Bug
  DistroRelease: Ubuntu 15.04
  Package: ntfs-3g 1:2013.1.13AR.1-2ubuntu3
  ProcVersionSignature: Ubuntu 3.16.0-25.33-generic 3.16.7
  Uname: Linux 3.16.0-25-generic x86_64
  ApportVersion: 2.15-0ubuntu1
  Architecture: amd64
  CurrentDesktop: Unity
  Date: Wed Dec  3 15:48:12 2014
  EcryptfsInUse: Yes
  InstallationDate: Installed on 2014-11-20 (13 days ago)
  InstallationMedia: Ubuntu 15.04 "Vivid Vervet" - Alpha amd64 (20141119)
  SourcePackage: ntfs-3g
  UpgradeStatus: No upgrade log present (probably fresh install)

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