kern/53683: mount_nfs and TCP hangs on msk(4)

[mrg%eterna.com.au@localhost]

>Number:         53683
>Category:       kern
>Synopsis:       mount_nfs and TCP hangs on msk(4)
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu Oct 25 04:50:01 +0000 2018
>Originator:     matthew green
>Release:        NetBSD 8.99.25
>Organization:
people's front against (bozotic) www (softwar foundation)
>Environment:
System: NetBSD soft-irony.eterna23.net 8.99.25 NetBSD 8.99.25 (_soft_) #76: Wed Oct 24 17:33:19 PDT 2018  mrg%space-bird.eterna23.net@localhost:/var/obj/evbarm-aarch64/usr/src/sys/arch/evbarm/compile/_soft_ evbarm
Architecture: aarch64
Machine: evbarm
>Description:

	i am able to reliably hang my NFS mounts on the softiron OD1000.
	when it happens, this error is printed:

	[ 5344.5949679] nfs_reply: ignoring error 55

	i guessed trying UDP mounts, and while i still get the error 55
	message (eg, about 10 times while unpacking fresh sets sourced
	from NFS), it works fine.

	while it may be an msk(4) bug, my ssh session remains active and
	working just fine while the NFS mount is hung, so it seems more
	likely to be either an msk vs NFS problem, or something in the
	NFS stack itself, than a pure msk(4) bug.

>How-To-Repeat:

	mount_nfs on OD1000.  make sure TCP is used.

>Fix: