deadlock bugfix for UFS needs testing. patch01

[Hiten Pandya]

There are a few more softdep related bugfixes, which exist in FreeBSD.  I 
have ported those and tested them in my tree, being tested.

I will release those on this list once I finalise them as working, about 
one more week of testing.  I would like those go into RELEASE if they are 
deemed to be stable.

			Hiten Pandya
			hmp at xxxxxxxxxxxxx
Matthew Dillon wrote:
    This patch is an attempt to fix a deadlock reported by Mitja Horvat
    while running rtorrent.  I vaguely recall seeing a similar bug report
    last year on rtorrent.
    Our best analysis of the problem seems to show a deadlock between a
    filesystem indirect block, a filesystem data block, and a VM page.
    This patch attempts to unwind the deadlock.
    The patch is somewhat dangerous simply due to the fact that it messes
    with filesystem internals, so I would like to make it available
    for wider testing for people who have test boxes setup that can afford
    to lose their lunch (aka filesystem blowups).  The patch is against HEAD.
						-Matt