Re: Freeing vnodes.
From: Jeff Roberson (jroberson_at_chesapeake.net)
Date: 03/29/05
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Date: Tue, 29 Mar 2005 03:06:02 -0500 (EST) To: David Schultz <das@FreeBSD.ORG>
On Tue, 29 Mar 2005, David Schultz wrote:
> On Tue, Mar 29, 2005, Jeff Roberson wrote:
> > On Tue, 29 Mar 2005, Jeff Roberson wrote:
> >
> > > On Mon, 28 Mar 2005, David Schultz wrote:
> > >
> > > > On Mon, Mar 28, 2005, Jeff Roberson wrote:
> > > > > > > I am worried about the v_dd,v_ddid fields of a directory B that has the
> > > > > > > to be released vnode A as parent. (Obviously in this case there is no
> > > > > > > namecache entry with the vnode A as the directory (nc_dvp))
> > > > > > >
> > > > > > > Right now A is type stable - but if A is released, access to B->v_dd
> > > > > > > may cause a page fault.
> > > > > > >
> > > > > > > Stephan
> > > > > >
> > > > > > Jeff,
> > > > > >
> > > > > > Do you plan to address the problem now that the code is checked in?
> > > > >
> > > > > Vnodes with children in the name cache are held with vhold() and not
> > > > > recycled.
> > > >
> > > > Yes, but cache_purge() is called directly in a number of places
> > > > where the vnode may have children, e.g. in mount. So dangling
> > > > references might still be possible unless cache_purge() fixes up
> > > > the children's v_dd pointers appropriately.
> > > >
> > >
> > > ah, indeed. How does this look:
> >
> > Also, are the ids really necessary now that we don't reuse vnodes?
> > Shouldn't the pointer be sufficient?
>
> I think so. The patch I sent you a few days ago gets rid of v_id
> except in vfs_cache_lookup(), where it is used to guarantee that
> the vnode hasn't changed while sleeping in vn_lock(). With vnode
> reclamation, that isn't safe anyway, so if you fix vfs_cache_lookup(),
> we can kill v_id completely.
You're right, cache_lookup() needs to be changed to return a referenced
vnode. There are only a few callers outside of vfs_cache.c that I'll have
to change. I'll put this on my todo list. After that v_id can go away.
I'll look at your patch again soon.
>
> Your patch looks okay at a glance, but shouldn't you be iterating over
> v_cache_src instead of v_cache_dst?
>
Yes, I thought I double checked that. I haven't done any name cache stuff
in a while, and I always get confused whether src means sources for this
vnode, or names this vnode is a source for.
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