kern/53423: Some zfs tests fail even on real hardware

[gson%gson.org@localhost (Andreas Gustafsson)]

>Number:         53423
>Category:       kern
>Synopsis:       Some zfs tests fail even on real hardware
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue Jul 03 18:35:00 +0000 2018
>Originator:     Andreas Gustafsson
>Release:        NetBSD-current, source date >= 2018-05-28
>Organization:

>Environment:
System: NetBSD
Architecture: x86_64
Machine: amd64
>Description:

Since the zfs updates of May 28, in addition to the memory size
related test failures reported in PR 53422, a few other zfs tests are
failing regardless on memory size, for example on a physical amd64
system with 32 GB RAM.  They are:

  fs/vfs/t_renamerace:zfs_renamerace
  fs/vfs/t_renamerace:zfs_renamerace_dirs
  fs/vfs/t_vnops:zfs_rename_reg_nodir

For log output from a recent test run, see

  http://www.gson.org/netbsd/bugs/build/amd64-baremetal/2018/2018.07.03.12.17.54/test.html#failed-tcs-summary

>How-To-Repeat:

Run the ATF tests on an amd64 system with at least 512 MB RAM.

>Fix: