Re: CVS commit: src/sys/kern

[Mindaugas Rasiukevicius <rmind%netbsd.org@localhost>]

Juergen Hannken-Illjes <hannken%eis.cs.tu-bs.de@localhost> wrote:
> > > > <...>
> > > > 
> > > > It's not obvious from your commit message what prevents it from
> > > > gaining a reference after the lock is dropped.
> > > 
> > > The interlock is taken before the freelist lock is dropped and vnodes
> > > on the free lists should never appear on other lists.
> > 
> > Not even the name cache?
> > 
> > (I can't remember off the top of my head, but IIRC there's something
> > sneaky about it)
> 
> Name cache does vtryget() then vget(). As the usecount is zero, vtryget()
> fails and vget() gets called with the interlock held and needs the
> freelist lock to proceed.
> 
> I still don't see a race here.

It would be quite cool to expand the comment in the top of vfs_subr.c, with
sections like "Vnode reclamation mechanism", "Vnode life-cycle", etc and
thus document our knowledge.  Now, each time we re-read and re-discover the
logic and potential corner cases.  And, I believe, not all corner cases.

Just thinking out load. :)

-- 
Mindaugas