Re: UVM/genfs review

[Andrew Doran <ad%netbsd.org@localhost>]

On Thu, Jan 08, 2009 at 09:12:55PM +0100, Juergen Hannken-Illjes wrote:

> On Thu, Jan 08, 2009 at 08:01:56PM +0100, Joerg Sonnenberger wrote:
> > Hi all,
> > given the state of netbsd-5, I would like to get the WAPBL patch
> > http://mail-index.netbsd.org/current-users/2008/10/31/msg005591.html
> > into HEAD and pull it up. For that I would really like to have review
> > from someone who understand UVM and/or genfs. The patch is likely to
> > break persistent snapshots with fss(4), but I don't think it will break
> > non-persistent ones (e.g. as used for backups).
> > 
> > Joerg
> 
> Just for the records, still strong objection from me.  As I told you before
> this would bring back a deadlock (see Rev. 1.12 of genfs_io.c).  We have
> to take the wapbl LOCK before we lock pages.  Therefore it will break
> ALL file system internal snapshots, persistent or not.

If this change introduces another deadlock or problem, even if it fixes
something else, don't submit it for pull-up as-is.

Be aware that there is an existing, related deadlock in genfs. (e-mail
me for details if interested in fixing it.)

Andrew