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

[Stanislav Kinsbursky <skinsbursky@parallels.com>]

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.

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;
 }