Okay, looks like I might have a *good* one here ... inode hang

[Tim Robbins]

On Mon, Jul 07, 2003 at 01:05:30AM -0700, David Schultz wrote:

> On Thu, Jul 03, 2003, Marc G. Fournier wrote:
> > > follow that one, too.  Maybe the trail will simply lead back to
> > > unionfs...
> > 
> > 'K, how about a loop?
> 
> Heh...it's a deadlock between unionfs and nullfs.  Sheesh.
> If unionfs is at fault here, I think I already know where
> the problem is, and it isn't easy to fix.  But I'll have to
> look more carefully when I get a chance.

nullfs on 4.x can probably deadlock in certain situations while attempting to
recycle vnodes; see null_vnops.c 1.63. This bug was made more obvious in
5.x by null_vnops.c 1.51, but I'm pretty sure that the problem was still
there in earlier versions, but was just harder to trigger.

There are a few questionable things in unionfs too. There might be a race in
union_inactive() (should it grab the vnode interlock before dropping
the vnode lock and call vgonel() instead of vgone()?), and the support for
locking stacks of vnodes seems to be #if 0'd out in union_lock().


Tim