RHEL7: NFS client stale submount remains in /proc/mounts due to due to periodic path_resolution operation even if the export has been removed on server

Solution Verified - Updated -

Issue

  • We use RHEL7 along with NetApp filers that provide NFS storage. These mount utilize the NetApp snapshot backup technology to do backups of the NAS mounts. We have been getting a lot reports recently where some hosts with NAS have the hidden .snapshot directory mounted on the host. Over time these snapshot backups are removed and the mounts then go stale do to them no longer existing. Such mounts are never removed on the NFS client but remain in /proc/mounts and visible.
    Example:
  df: '/mnt/netapp/.snapshot/hourly.2018-01-15_2200': Stale file handle
  • Basically you cd into the .snapshot directory on the NAS mount and do something like a ls and the .snapshot directory automounts and doesn’t go away. So temp fix is to just umount the stale mounts and they go away.

Environment

  • Red Hat Enteprise Linux 7.4 (NFS client)
    • kernels before kernel-3.10.0-1062.el7
    • non-autofs mounted NFS submounts that are mounted by crossing over via a path_resolution operation
  • NFS server
    • Seen with NetApp .snapshot directories
    • May occur with any NFS server where submounts get destroyed while mounted on NFS client

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