[Bug 1868708] [NEW] mdmon: device descriptor is not closed

[Mariusz Tkaczyk]

Public bug reported:

When device disappears from the system "mdadm -If" is triggered by udev
and drive is removed from the corresponding array and container. The
missing close() in metadata manager (mdmon) causes that userspace
handler to the device is still opened (can be tracked by lsof -p
<mdmon_pid>).

For nvme drives it causes weird namespace number after hot-plug (e.g. will appear nvme1n2). The issue affects only IMSM metadata format.
Reproducible on Focal with latest mdadm 4.1-5ubuntu1.

Steps:
1. Create IMSM container:
#mdadm -CR imsm -e imsm -n2 /dev/nvme[01]n1
2. Create IMSM array:
#mdadm -CR vol1 -l1 -n2 /dev/nvme[01]n1
3. remove via sysfs drive:
#echo 1 > /sys/block/nvme0n1/device/device/remove
4. restore the same drive:
#echo 1 > /sys/bus/pci/rescan
5. see mdstat and lsblk:
# cat /proc/mdstat

Result:
/dev/nvme0n2 appears in system.

** Affects: mdadm (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: patch-accepted-upstream

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https://bugs.launchpad.net/bugs/1868708

Title:
  mdmon: device descriptor is not closed

Status in mdadm package in Ubuntu:
  New

Bug description:
  When device disappears from the system "mdadm -If" is triggered by
  udev and drive is removed from the corresponding array and container.
  The missing close() in metadata manager (mdmon) causes that userspace
  handler to the device is still opened (can be tracked by lsof -p
  <mdmon_pid>).

  For nvme drives it causes weird namespace number after hot-plug (e.g. will appear nvme1n2). The issue affects only IMSM metadata format.
  Reproducible on Focal with latest mdadm 4.1-5ubuntu1.

  Steps:
  1. Create IMSM container:
  #mdadm -CR imsm -e imsm -n2 /dev/nvme[01]n1
  2. Create IMSM array:
  #mdadm -CR vol1 -l1 -n2 /dev/nvme[01]n1
  3. remove via sysfs drive:
  #echo 1 > /sys/block/nvme0n1/device/device/remove
  4. restore the same drive:
  #echo 1 > /sys/bus/pci/rescan
  5. see mdstat and lsblk:
  # cat /proc/mdstat

  Result:
  /dev/nvme0n2 appears in system.

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