misc/161016: umount doesn't fully sync UFS filesystems on 9.x

Garrett Cooper gcooper at ixsystems.com
Sun Sep 25 18:50:09 UTC 2011

>Number:         161016
>Category:       misc
>Synopsis:       umount doesn't fully sync UFS filesystems on 9.x
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-bugs
>State:          open
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Sun Sep 25 18:50:08 UTC 2011
>Originator:     Garrett Cooper
>Release:        9.0-BETA2
iXsystems, Inc.
FreeBSD fallout.local 9.0-BETA2 FreeBSD 9.0-BETA2 #10 r225587M: Thu Sep 15 09:07:08 PDT 2011     root at fallout.local:/usr/obj/usr/src/sys/FALLOUT  amd64
As discussed here [1] and here [2], there appears to be a bug in how data is being synced out to memory disks in the base system which causes repeated builds in nanobsd to fail unless adds 2 explicit sync's before each umount operation is performed; this is odd because umount(8) explicitly sync's unless -f is specified (previously, it explicitly called sync whenever umount was called -- see http://svnweb.freebsd.org/base?view=revision&revision=222466 ).

I've run into this bug where the underlying storage used for the vnode disk is either housed on UFS or ZFS, which suggests that the vnode backed disk is the problem child.

FreeNAS uses UFS1 SU (we don't modify the arguments passed via the $NANO_NEWFS var), but lev@ also reported that he ran into issues with UFS2 SU, which suggests that it's a generic syncing problem with UFS + SU and/or how md(4)s sync outstanding writes out to disk.

1. http://www.mavetju.org/mail/view_message.php?list=freebsd-embedded&id=3382579&raw=yes
2. http://comments.gmane.org/gmane.os.freebsd.current/135617



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