Re: [PATCH v3] NFSd: set nfsd_serv to NULL after service destruction

["J. Bruce Fields" <bfields@fieldses.org>]

On Tue, Jul 03, 2012 at 04:46:41PM +0400, Stanislav Kinsbursky wrote:
> v3:
> 1) Rebased for 3.6 kernel.
> 
> v2:
> 1) Set global nfsd_serv pointer to NULL only if no running threads left.
> 
> Otherwise we will get NULL pointer dereference on last thread exit in
> nfsd_last_thread().
> This patch also introduces nfsd_destroy() helper for per-net NFSd shutdown.

That last step should really be done in a separate patch, then the
bugfix done after that.

But I'm confused: I'm not seeing the NULL dereference.
nfsd_last_thread doesn't use nfsd_serv as far as I can tell.

--b.

> 
> Signed-off-by: Stanislav Kinsbursky <skinsbursky@parallels.com>
> ---
>  fs/nfsd/nfsctl.c |    8 ++------
>  fs/nfsd/nfsd.h   |   11 +++++++++++
>  fs/nfsd/nfssvc.c |   24 ++++++++----------------
>  3 files changed, 21 insertions(+), 22 deletions(-)
> 
> diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
> index c55298e..fa49cff 100644
> --- a/fs/nfsd/nfsctl.c
> +++ b/fs/nfsd/nfsctl.c
> @@ -673,9 +673,7 @@ static ssize_t __write_ports_addfd(char *buf)
>  
>  	err = svc_addsock(nfsd_serv, fd, buf, SIMPLE_TRANSACTION_LIMIT);
>  	if (err < 0) {
> -		if (nfsd_serv->sv_nrthreads == 1)
> -			svc_shutdown_net(nfsd_serv, net);
> -		svc_destroy(nfsd_serv);
> +		nfsd_destroy(net);
>  		return err;
>  	}
>  
> @@ -744,9 +742,7 @@ out_close:
>  		svc_xprt_put(xprt);
>  	}
>  out_err:
> -	if (nfsd_serv->sv_nrthreads == 1)
> -		svc_shutdown_net(nfsd_serv, net);
> -	svc_destroy(nfsd_serv);
> +	nfsd_destroy(net);
>  	return err;
>  }
>  
> diff --git a/fs/nfsd/nfsd.h b/fs/nfsd/nfsd.h
> index 1671429..1336a65 100644
> --- a/fs/nfsd/nfsd.h
> +++ b/fs/nfsd/nfsd.h
> @@ -73,6 +73,17 @@ int		nfsd_nrpools(void);
>  int		nfsd_get_nrthreads(int n, int *);
>  int		nfsd_set_nrthreads(int n, int *);
>  
> +static inline void nfsd_destroy(struct net *net)
> +{
> +	int destroy = (nfsd_serv->sv_nrthreads == 1);
> +
> +	if (destroy)
> +		svc_shutdown_net(nfsd_serv, net);
> +	svc_destroy(nfsd_serv);
> +	if (destroy)
> +		nfsd_serv = NULL;
> +}
> +
>  #if defined(CONFIG_NFSD_V2_ACL) || defined(CONFIG_NFSD_V3_ACL)
>  #ifdef CONFIG_NFSD_V2_ACL
>  extern struct svc_version nfsd_acl_version2;
> diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
> index ee709fc..240473c 100644
> --- a/fs/nfsd/nfssvc.c
> +++ b/fs/nfsd/nfssvc.c
> @@ -254,8 +254,6 @@ static void nfsd_shutdown(void)
>  
>  static void nfsd_last_thread(struct svc_serv *serv, struct net *net)
>  {
> -	/* When last nfsd thread exits we need to do some clean-up */
> -	nfsd_serv = NULL;
>  	nfsd_shutdown();
>  
>  	svc_rpcb_cleanup(serv, net);
> @@ -332,6 +330,7 @@ static int nfsd_get_default_max_blksize(void)
>  int nfsd_create_serv(void)
>  {
>  	int error;
> +	struct net *net = current->nsproxy->net_ns;
>  
>  	WARN_ON(!mutex_is_locked(&nfsd_mutex));
>  	if (nfsd_serv) {
> @@ -346,7 +345,7 @@ int nfsd_create_serv(void)
>  	if (nfsd_serv == NULL)
>  		return -ENOMEM;
>  
> -	error = svc_bind(nfsd_serv, current->nsproxy->net_ns);
> +	error = svc_bind(nfsd_serv, net);
>  	if (error < 0) {
>  		svc_destroy(nfsd_serv);
>  		return error;
> @@ -427,11 +426,7 @@ int nfsd_set_nrthreads(int n, int *nthreads)
>  		if (err)
>  			break;
>  	}
> -
> -	if (nfsd_serv->sv_nrthreads == 1)
> -		svc_shutdown_net(nfsd_serv, net);
> -	svc_destroy(nfsd_serv);
> -
> +	nfsd_destroy(net);
>  	return err;
>  }
>  
> @@ -478,9 +473,7 @@ out_shutdown:
>  	if (error < 0 && !nfsd_up_before)
>  		nfsd_shutdown();
>  out_destroy:
> -	if (nfsd_serv->sv_nrthreads == 1)
> -		svc_shutdown_net(nfsd_serv, net);
> -	svc_destroy(nfsd_serv);		/* Release server */
> +	nfsd_destroy(net);		/* Release server */
>  out:
>  	mutex_unlock(&nfsd_mutex);
>  	return error;
> @@ -563,12 +556,13 @@ nfsd(void *vrqstp)
>  	nfsdstats.th_cnt --;
>  
>  out:
> -	if (rqstp->rq_server->sv_nrthreads == 1)
> -		svc_shutdown_net(rqstp->rq_server, &init_net);
> +	rqstp->rq_server = NULL;
>  
>  	/* Release the thread */
>  	svc_exit_thread(rqstp);
>  
> +	nfsd_destroy(&init_net);
> +
>  	/* Release module */
>  	mutex_unlock(&nfsd_mutex);
>  	module_put_and_exit(0);
> @@ -682,9 +676,7 @@ int nfsd_pool_stats_release(struct inode *inode, struct file *file)
>  
>  	mutex_lock(&nfsd_mutex);
>  	/* this function really, really should have been called svc_put() */
> -	if (nfsd_serv->sv_nrthreads == 1)
> -		svc_shutdown_net(nfsd_serv, net);
> -	svc_destroy(nfsd_serv);
> +	nfsd_destroy(net);
>  	mutex_unlock(&nfsd_mutex);
>  	return ret;
>  }
>