RHEL6.3: kernel hang / soft lockup under heavy NFS4 load, events kernel thread stuck in umount_tree holding vfsmount_lock

Solution Unverified - Updated -

Issue

  • While testing the nfsv4 client provided in RHEL 6, the machine displays a load of 2000 in top for a while and suddenly the server reboots without any warning.
  • Same test script runs fine on a different NFS client machine
  • The /var/log/messages files are getting filled with "soft lockup" errors.
  • High nfs thread count / nfsd thread count

Environment

  • Red Hat Enterprise Linux 6.2 - 6.4
    • Seen on RHEL6.2 / 6.3 kernels prior to kernel-2.6.32-358.18.1.el6
  • Not specific to NFS version
  • Thousands of NFS automounts
  • Seen on RHEL NFS client to Solaris OpenIndiana NFS server over NFSv4

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