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

[Kirk McKusick]

> Date: Thu, 29 Sep 2011 17:40:43 +0200
> Subject: Re: Need to force sync(2) before umounting UFS1 filesystems?
> From: Attilio Rao <attilio at freebsd.org>
> To: Kirk McKusick <mckusick at mckusick.com>
> Cc: Garrett Cooper <yanegomi at gmail.com>, freebsd-fs at freebsd.org,
>         Xin LI <delphij at freebsd.org>
> 
> 2011/9/29 Kirk McKusick <mckusick at mckusick.com>:
> 
> > Thanks for providing a bit more of the history on this codepath.
> >
> > Since 9-stable has now been branched, I believe that the best path
> > forward is to check this change into head and let it sit there for
> > several months so that we can get some experience with it. If it
> > causes folks problems we can back it out. If it does not cause
> > problems, then we can MFC it to 9-stable.
> >
> > Does this seem like a reasonable approach?
> 
> In general yes, but I'd like to understand why unmount should fail so
> much with SU... do we do extended period with vfs_busy()'ed
> filesystem?
> 
> I need more context here, likely I'd need to look into the PRs too
> before to give an informative answer.
> 
> Attilio

I am definitely not in a rush on this, so by all means take some time
to look it over. The EBUSY unmount has been in its current state
for several years, so I am fine with taking a few weeks to sort out
the correct solution. Indeed, I am glad that Garrett has volunteered
to do some more serious testing.

If this general approach is not correct, I can put a hook in for just
UFS so that it can have its historic behavior. As you have noted, the
SU code has a lot of activity that gets done under the protection of
vfs_busy. So it may be the only filesystem for which draining the
vfs_busy lock during unmount is needed.

Will you be at the EuroBSD conference next week? If so we can discuss
this there.

> Date: Thu, 29 Sep 2011 08:38:59 -0700
> Subject: Re: Need to force sync(2) before umounting UFS1 filesystems?
> From: Garrett Cooper <yanegomi at gmail.com>
> To: Kirk McKusick <mckusick at mckusick.com>
> Cc: Attilio Rao <attilio at freebsd.org>, freebsd-fs at freebsd.org,
>     Xin LI <delphij at freebsd.org>
> 
> > Does this seem like a reasonable approach?
> 
> I'll give it a quick run through first on some machines this weekend,
> with NFS, UFS, and ZFS. It seems like this could negatively affect a
> number of users, so I want to make sure that it passes a smoke test
> before committing directly to HEAD.
> 
> Thanks!
> -Garrett

Thanks for doing these tests to help us find out if there are landmines
in this change.

	Kirk McKusick