nfsd: make nfsd_svc take an array of thread counts

Now that the refcounting is fixed, rework nfsd_svc to use the same
thread setup as the pool_threads interface. Have it take an array of
thread counts instead of just a single value, and pass that from the
netlink threads set interface.  Since the new netlink interface doesn't
have the same restriction as pool_threads, move the guard against
shutting down all threads to write_pool_threads.
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/nfsd/nfsctl.c

@@ -406,7 +406,7 @@ static ssize_t write_threads(struct file *file, char *buf, size_t size)
 			return -EINVAL;
 		trace_nfsd_ctl_threads(net, newthreads);
 		mutex_lock(&nfsd_mutex);
-		rv = nfsd_svc(newthreads, net, file->f_cred, NULL);
+		rv = nfsd_svc(1, &newthreads, net, file->f_cred, NULL);
 		mutex_unlock(&nfsd_mutex);
 		if (rv < 0)
 			return rv;
@@ -481,6 +481,14 @@ static ssize_t write_pool_threads(struct file *file, char *buf, size_t size)
 				goto out_free;
 			trace_nfsd_ctl_pool_threads(net, i, nthreads[i]);
 		}
+
+		/*
+		 * There must always be a thread in pool 0; the admin
+		 * can't shut down NFS completely using pool_threads.
+		 */
+		if (nthreads[0] == 0)
+			nthreads[0] = 1;
+
 		rv = nfsd_set_nrthreads(i, nthreads, net);
 		if (rv)
 			goto out_free;
@@ -1696,7 +1704,7 @@ int nfsd_nl_threads_set_doit(struct sk_buff *skb, struct genl_info *info)
 			scope = nla_data(attr);
 	}
 
-	ret = nfsd_svc(nthreads, net, get_current_cred(), scope);
+	ret = nfsd_svc(1, &nthreads, net, get_current_cred(), scope);
 
 out_unlock:
 	mutex_unlock(&nfsd_mutex);

fs/nfsd/nfsd.h

@@ -103,7 +103,8 @@ bool		nfssvc_encode_voidres(struct svc_rqst *rqstp,
 /*
  * Function prototypes.
  */
-int		nfsd_svc(int nrservs, struct net *net, const struct cred *cred, const char *scope);
+int		nfsd_svc(int n, int *nservers, struct net *net,
+			 const struct cred *cred, const char *scope);
 int		nfsd_dispatch(struct svc_rqst *rqstp);
 
 int		nfsd_nrthreads(struct net *);

fs/nfsd/nfssvc.c

@@ -709,6 +709,19 @@ int nfsd_get_nrthreads(int n, int *nthreads, struct net *net)
 	return 0;
 }
 
+/**
+ * nfsd_set_nrthreads - set the number of running threads in the net's service
+ * @n: number of array members in @nthreads
+ * @nthreads: array of thread counts for each pool
+ * @net: network namespace to operate within
+ *
+ * This function alters the number of running threads for the given network
+ * namespace in each pool. If passed an array longer then the number of pools
+ * the extra pool settings are ignored. If passed an array shorter than the
+ * number of pools, the missing values are interpreted as 0's.
+ *
+ * Returns 0 on success or a negative errno on error.
+ */
 int nfsd_set_nrthreads(int n, int *nthreads, struct net *net)
 {
 	int i = 0;
@@ -716,11 +729,18 @@ int nfsd_set_nrthreads(int n, int *nthreads, struct net *net)
 	int err = 0;
 	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
 
-	WARN_ON(!mutex_is_locked(&nfsd_mutex));
+	lockdep_assert_held(&nfsd_mutex);
 
 	if (nn->nfsd_serv == NULL || n <= 0)
 		return 0;
 
+	/*
+	 * Special case: When n == 1, pass in NULL for the pool, so that the
+	 * change is distributed equally among them.
+	 */
+	if (n == 1)
+		return svc_set_num_threads(nn->nfsd_serv, NULL, nthreads[0]);
+
 	if (n > nn->nfsd_serv->sv_nrpools)
 		n = nn->nfsd_serv->sv_nrpools;
 
@@ -743,13 +763,6 @@ int nfsd_set_nrthreads(int n, int *nthreads, struct net *net)
 		}
 	}
 
-	/*
-	 * There must always be a thread in pool 0; the admin
-	 * can't shut down NFS completely using pool_threads.
-	 */
-	if (nthreads[0] == 0)
-		nthreads[0] = 1;
-
 	/* apply the new numbers */
 	for (i = 0; i < n; i++) {
 		err = svc_set_num_threads(nn->nfsd_serv,
@@ -761,13 +774,19 @@ int nfsd_set_nrthreads(int n, int *nthreads, struct net *net)
 	return err;
 }
 
-/*
- * Adjust the number of threads and return the new number of threads.
- * This is also the function that starts the server if necessary, if
- * this is the first time nrservs is nonzero.
+/**
+ * nfsd_svc: start up or shut down the nfsd server
+ * @n: number of array members in @nthreads
+ * @nthreads: array of thread counts for each pool
+ * @net: network namespace to operate within
+ * @cred: credentials to use for xprt creation
+ * @scope: server scope value (defaults to nodename)
+ *
+ * Adjust the number of threads in each pool and return the new
+ * total number of threads in the service.
  */
 int
-nfsd_svc(int nrservs, struct net *net, const struct cred *cred, const char *scope)
+nfsd_svc(int n, int *nthreads, struct net *net, const struct cred *cred, const char *scope)
 {
 	int	error;
 	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
@@ -777,13 +796,6 @@ nfsd_svc(int nrservs, struct net *net, const struct cred *cred, const char *scop
 
 	dprintk("nfsd: creating service\n");
 
-	nrservs = max(nrservs, 0);
-	nrservs = min(nrservs, NFSD_MAXSERVS);
-	error = 0;
-
-	if (nrservs == 0 && nn->nfsd_serv == NULL)
-		goto out;
-
 	strscpy(nn->nfsd_name, scope ? scope : utsname()->nodename,
 		sizeof(nn->nfsd_name));
 
@@ -795,7 +807,7 @@ nfsd_svc(int nrservs, struct net *net, const struct cred *cred, const char *scop
 	error = nfsd_startup_net(net, cred);
 	if (error)
 		goto out_put;
-	error = svc_set_num_threads(serv, NULL, nrservs);
+	error = nfsd_set_nrthreads(n, nthreads, net);
 	if (error)
 		goto out_put;
 	error = serv->sv_nrthreads;