Re: [PATCH 0/5 v2] sunrpc: stop refcounting svc_serv

[Jeff Layton <jlayton@kernel.org>]

On Fri, 2023-12-15 at 14:19 +0000, Chuck Lever III wrote:
> > On Dec 15, 2023, at 5:59 AM, Jeff Layton <jlayton@kernel.org> wrote:
> > 
> > On Fri, 2023-12-15 at 11:56 +1100, NeilBrown wrote:
> > > I sent an earlier version of this series, got some feed back, revised
> > > it, but never sent it again.  Sorry.
> > > 
> > > The main feedback was around the interaction between sunrpc and nfsd for
> > > handling poolstats.  I have changed that so that nfsd tells sunrpc where
> > > the svc_serv pointer lives, and where to find a mutex to protect it.
> > > sunrpc then taks the mutex and accesses the pointer - if not NULL.  I
> > > think this is nicer than the version that pass around funciton pointers.
> > > 
> > > This series is against nfsd-next
> > > 
> > > Thanks,
> > > NeilBrown
> > > 
> > > 
> > > [PATCH 1/5] nfsd: call nfsd_last_thread() before final nfsd_put()
> > > [PATCH 2/5] svc: don't hold reference for poolstats, only mutex.
> > > [PATCH 3/5] nfsd: hold nfsd_mutex across entire netlink operation
> > > [PATCH 4/5] SUNRPC: discard sv_refcnt, and svc_get/svc_put
> > > [PATCH 5/5] nfsd: rename nfsd_last_thread() to nfsd_destroy_serv()
> > 
> > I'm not sure patch #2 is better than the version with function pointers,
> > but it seems reasonable.
> > 
> > Note that patch #1 probably needs to go to v6.6 stable, and I think we
> > want #3 in v6.7 before it ships.
> 
> Remind me why #3 should go into v6.7-rc ? There's no Fixes tag on
> that one.
> 
> 

It's the problem I noted to Lorenzo the other day:

   
https://lore.kernel.org/linux-nfs/5d9bbb599569ce29f16e4e0eef6b291eda0f375b.camel@kernel.org/T/#u

Once you've dropped the nfsd_mutex, there is no guarantee that
nn->nfsd_serv will still be a valid pointer. Holding the mutex across
the operation (like Neil's patch does), should close the race.

-- 
Jeff Layton <jlayton@kernel.org>