Need to force sync(2) before umounting UFS1 filesystems?

[Kostik Belousov]

On Sun, Oct 09, 2011 at 03:37:22PM -0700, Garrett Cooper wrote:
> On Sun, Oct 9, 2011 at 3:22 PM, Garrett Cooper <yanegomi at gmail.com> wrote:
> > On Sat, Oct 1, 2011 at 2:37 PM, Kirk McKusick <mckusick at mckusick.com> wrote:
> >>> Date: Sat, 1 Oct 2011 12:44:04 -0700
> >>> Subject: Re: Need to force sync(2) before umounting UFS1 filesystems?
> >>> From: Garrett Cooper <yanegomi at gmail.com>
> >>> To: Attilio Rao <attilio at freebsd.org>
> >>> Cc: Kostik Belousov <kostikbel at gmail.com>,
> >>>         Kirk McKusick <mckusick at mckusick.com>, freebsd-fs at freebsd.org,
> >>>         Xin LI <delphij at freebsd.org>
> >>>
> >>> Ok. Now that I know this is the direction you guys want to go, I'll
> >>> start testing the change.
> >>
> >> Thanks for throwing some testing at this. Please test my latest
> >> proposed change (included below so you do not have to dig through
> >> earlier email) as I believe that it has the least likelyhood of
> >> problems and is what I am currently proposing to put in.
> >
> > I apologize for not getting this done sooner. It passes a smoke test
> > with the following filesystems:
> >
> > nfs
> > nullfs
> > smbfs
> > unionfs
> > ufs
> > zfs
> >
> > I'll be running more extensive stress tests soon, but it looks like a
> > good step forward.
> 
> Forgot to note: my FreeNAS builds nanobsd no longer fail with the
> attached patch after I remove my sync hacks :).

The real case to test is the NFS mount which is wedged due to
hung/unresponsive NFS server. I have high suspect that the patch
could introduce the unkillable hung unmount process.
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