Recursive nullfs mounts and r224655

[Kostik Belousov]

On Sat, Aug 06, 2011 at 08:11:32PM -0400, b. f. wrote:
> On 8/6/11, Kostik Belousov <kostikbel at gmail.com> wrote:
> > On Sat, Aug 06, 2011 at 04:44:25AM -0400, b. f. wrote:
> >> Recent changes to the kernel (sys/kern/vfs_mount.c, in r224655?)
> >> between r224550 and r224655 have broken my tinderbox setup.  It had a
> >> tmpfs filesystem mounted at /T and a UFS filesystem mounted at /U,
> >> and, when setting up the tinderbox, performed:
> >>
> >> mkdir /U/u1
> >> mkdir /U/u2
> >> mkdir /T/t1
> >> mount -t nullfs /T/t1 /U/u1
> >> mkdir-p /U/u1/u3/u4
> >> mount -t nullfs /U/u2 /U/u1/u3/u4
> >> ...
> >>
> >> This worked at r224550 and before.  It now fails at the second nullfs
> >> mount, with ENOENT("mount_nullfs: No such file or directory").
> > r224615 and r224655 must be reverted.
> >
> > The reason for your trouble is that nullfs cannot cache any vnodes,
> > thus reclaiming anything that get reference count of 0. This interacts
> > badly with VOP_VNTOCNP() which has to operate on the vnodes with
> > zero refcount, since we cannot decrement refcount under the namecache
> > lock.
> >
> > Trying to update vptocnp(9) interface is too intrusive change for freeze
> > period.
> >
> 
> 
> Thank you for the analysis, it will make fixing this problem locally a
> bit easier, while you sort it out.  Does 224614 have a bearing on this
> problem, as well as 224615?
> 
> b.
You are right, r224614 and r224655 are revisions that shall be reverted.
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