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Date: Sat, 13 Dec 2003 23:16:08 -0800 (PST)
From: Don Lewis <truckman@FreeBSD.org>
To: jroberson@chesapeake.net
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Subject: Re: HAVE TRACE & DDB Re: FreeBSD 5.2-RC1 released
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On 13 Dec, Don Lewis wrote:
> On 12 Dec, Jeff Roberson wrote:
> 
> 
>> fsync: giving up on dirty: 0xc4e18000: tag devfs, type VCHR, usecount 44,
>> writecount 0, refcount 14, flags (VI_XLOCK|VV_OBJBUF), lock type devfs: EXCL
>> (count 1) by thread 0xc20ff500
> 
> Why are we trying to reuse a vnode with a usecount of 44 and a refcount
> of 14?  What is thread 0xc20ff500 doing?

Following up to myself ...

It looks like we're trying to recycle this vnode because of the
following sysinstall code, in distExtractTarball():

    if (is_base && RunningAsInit && !Fake) {
        unmounted_dev = 1;
        unmount("/dev", MNT_FORCE);
    } else
        unmounted_dev = 0;

I'm guessing that the purpose of this code is to unmount devfs from /dev
so that when the base distribution is unpacked it can populate /dev from
the tarball.  This seems wrong, because it looks like the root file
system is mounted on /mnt, and devfs is also mounted on /mnt/dev ...

What happens if we forceably umount /dev while /dev/whatever holds a
mounted file system?  It looks like this is handled by vgonechrl().  It
looks to me like vclean() is going to do some scary stuff to this vnode.

BTW, I think the root vnode is the root of the md file system, not the
root of the file system being populated by sysinstall.  I don't know why
there would be anything to sync at this point, though.

I suspect that removing the above sysinstall code will fix the immediate
problem, but there is still much I don't understand.