Re: NFS panic

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Sat, Nov 10, 2012 at 05:33:47PM +0100, J. Hannken-Illjes wrote:
> On Nov 10, 2012, at 12:20 PM, Manuel Bouyer 
> <bouyer%antioche.eu.org@localhost> wrote:
> 
> > On Thu, Nov 08, 2012 at 12:45:55PM +0100, J. Hannken-Illjes wrote:
> >> To make it short, Manuels fix was right, me removing it and trying to get 
> >> it
> >> done in vn_lock() is wrong.
> >> 
> >> While vget() vs. cleanvnode() (the cleaner) was always free of races,
> >> vget() vs. vrelel() is not.  Manuels fix checking the vnode state when 
> >> vrelel()
> >> got its vnode lock and before it starts inactivating and cleaning is right.
> >> 
> >> Please try the attached diff that brings back the fix.
> > 
> > I'm not sure how this would fix it. Although there may also be a race
> > bwteen vget() and vrelel(), the race I described is really between
> > vget() and cleanvnode() here (more specifically, vget() and vclean(), which 
> > is
> > used by both cleanvnode() and vrelel()). I can't see how your patch would 
> > fix
> > this one.
> 
> I still don't get it.  If vget() gets preempted after releasing the nodes
> interlock this node has already been removed from the freelist so cleanvnode()
> cannot take and clean it.

Looks like you're right. the thread which did clean the vnode in the back of
vget was probably another one ...

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--