kern/52254: nfs unmount "locks up" if remote nfs host died since nfs_mount

[mlr%rse.com@localhost]

>Number:         52254
>Category:       kern
>Synopsis:       nfs unmount "locks up" if remote nfs host died since nfs_mount
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue May 23 18:50:00 +0000 2017
>Originator:     Michael L. Riechers
>Release:        NetBSD 7.1_RC2
>Organization:
M L Riechers Systems Engineering
Kind Regards, I am

 /s/ Michael L. Riechers

Michael L. Riechers,
Owner,					M L Riechers Systems Engineering
513/844-2220 (voice)			530 Main Street
513/205-5589 (cell)			Hamilton, Ohio 45013
mlr%rse.com@localhost  (internet)
www.rse.com  (WEB)

Systems Programming: The three most adverse malignancies in life are:
  1)signed numbers,  2)floating point numbers, and  3)little endians.

"Defend the Spirit of the Enlightenment."  Macron, 2017
>Environment:
	
	
System: NetBSD mterm.rse.com 7.1_RC2 NetBSD 7.1_RC2 (HOUSE-7.1_RC2) #0: Sun Feb 26 11:56:07 EST 2017 root%cterm.rse.com@localhost:/usr/local/src/usr/usr.201702210824Z/src/sys/arch/amd64/compile/obj/HOUSE-7.1_RC2 amd64
Architecture: x86_64
Machine: amd64
>Description:
	
A few weeks ago one of our computers bit the big one: the root disc
drive croaked (bad).  One of these days I'll get to replacing the
drive, but I'm not shedding too many tears, for 1)it's a little used
system, and 2) the important data was on other drives.

What is annoying is, however, the fact that we had files nfs mounted
on our network that were serviced from this computer.  Now any time we
do a "df", an unmount, or any operation that references the nfs from
that computer, the program "locks up," and ps shows:

             D       Marks a process in device or other short term,
                     uninterruptible wait.

I did a "df" on one of our computers a couple of weeks ago, and ps
still shows the process in device or other short term, uninterruptible
wait.  So much for short term.

I believe that the df inquiry is going to wait forever, demanding to
palaver with the nfs that isn't there anymore.  (It's inconvenient to
try to remember to do a "df -l," and of course, there goes info
concerning my other nfs mounts.)

I tried a "umount -fh mydeadcomputer.com" on the nfs mount, but all
that got me was a locked-up "umount."

I tried a "umount -fR themount-point" on the nfs mount, but all that
got me was a locked-up "umount."

I've tried starting up another computer to imitate the failed one as
to IP and interface name, but that didn't work.  It looks like the
only thing that will satisfy my live computers is an actual commune
with the dead nfs system (or a reboot).
>How-To-Repeat:
	
1.  Mount an nfs system on some remote computer's fs.
2.  Kill the remote computer.
3.  Attemt an unmount of the nfs mount.
4.  Pray that you have an alternative way to login, for yours is now locked up.
>Fix:
	
Reboot the local computer, or alternatively, beat the nfs driver with an axe.

>Unformatted:
 nfs unmount "locks up" if remote nfs host died since nfs_mount