Re: [PATCH 1/5] nfsd: call nfsd_last_thread() before final nfsd_put()

[Jeff Layton <jlayton@kernel.org>]

On Mon, 2023-10-30 at 12:08 +1100, NeilBrown wrote:
> If write_ports_addfd or write_ports_addxprt fail, they call nfsD_put()
> without calling nfsd_last_thread().  This leaves nn->nfsd_serv pointing
> to a structure that has been freed.
> 
> So export nfsd_last_thread() and call it when the nfsd_serv is about to
> be destroy.
> 
> Signed-off-by: NeilBrown <neilb@suse.de>
> ---
>  fs/nfsd/nfsctl.c | 9 +++++++--
>  fs/nfsd/nfsd.h   | 1 +
>  fs/nfsd/nfssvc.c | 2 +-
>  3 files changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
> index 739ed5bf71cd..79efb1075f38 100644
> --- a/fs/nfsd/nfsctl.c
> +++ b/fs/nfsd/nfsctl.c
> @@ -705,8 +705,10 @@ static ssize_t __write_ports_addfd(char *buf, struct net *net, const struct cred
>  
>  	err = svc_addsock(nn->nfsd_serv, net, fd, buf, SIMPLE_TRANSACTION_LIMIT, cred);
>  
> -	if (err >= 0 &&
> -	    !nn->nfsd_serv->sv_nrthreads && !xchg(&nn->keep_active, 1))
> +	if (err < 0 && !nn->nfsd_serv->sv_nrthreads && !nn->keep_active)
> +		nfsd_last_thread(net);
> +	else if (err >= 0 &&
> +		 !nn->nfsd_serv->sv_nrthreads && !xchg(&nn->keep_active, 1))
>  		svc_get(nn->nfsd_serv);
>  
>  	nfsd_put(net);
> @@ -757,6 +759,9 @@ static ssize_t __write_ports_addxprt(char *buf, struct net *net, const struct cr
>  		svc_xprt_put(xprt);
>  	}
>  out_err:
> +	if (!nn->nfsd_serv->sv_nrthreads && !nn->keep_active)
> +		nfsd_last_thread(net);
> +
>  	nfsd_put(net);
>  	return err;
>  }
> diff --git a/fs/nfsd/nfsd.h b/fs/nfsd/nfsd.h
> index f5ff42f41ee7..3286ffacbc56 100644
> --- a/fs/nfsd/nfsd.h
> +++ b/fs/nfsd/nfsd.h
> @@ -155,6 +155,7 @@ int nfsd_vers(struct nfsd_net *nn, int vers, enum vers_op change);
>  int nfsd_minorversion(struct nfsd_net *nn, u32 minorversion, enum vers_op change);
>  void nfsd_reset_versions(struct nfsd_net *nn);
>  int nfsd_create_serv(struct net *net);
> +void nfsd_last_thread(struct net *net);
>  
>  extern int nfsd_max_blksize;
>  
> diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
> index d6122bb2d167..6c968c02cc29 100644
> --- a/fs/nfsd/nfssvc.c
> +++ b/fs/nfsd/nfssvc.c
> @@ -542,7 +542,7 @@ static struct notifier_block nfsd_inet6addr_notifier = {
>  /* Only used under nfsd_mutex, so this atomic may be overkill: */
>  static atomic_t nfsd_notifier_refcount = ATOMIC_INIT(0);
>  
> -static void nfsd_last_thread(struct net *net)
> +void nfsd_last_thread(struct net *net)
>  {
>  	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
>  	struct svc_serv *serv = nn->nfsd_serv;

This patch should fix the problem that I was seeing with write_ports,
but it won't fix the hinky error cleanup in nfsd_svc. It looks like that
does get fixed in patch #4 though, so I'm not too concerned.

Reviewed-by: Jeff Layton <jlayton@kernel.org>