knfsd: Replace lock_kernel with a mutex in nfsd pool stats.

lock_kernel() in knfsd was replaced with a mutex. The later
commit 03cf6c9f49a8fea953d38648d016e3f46e814991 ("knfsd:
add file to export stats about nfsd pools") did not follow
that change. This patch fixes the issue.

Also move the get and put of nfsd_serv to the open and close methods
(instead of start and stop methods) to allow atomic check and increment
of reference count in the open method (where we can still return an
error).

Signed-off-by: Ryusei Yamaguchi <mandel59@gmail.com>
Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Cc: Greg Banks <gnb@fmeh.org>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>

fs/nfsd/nfsctl.c

@@ -174,12 +174,13 @@ static const struct file_operations exports_operations = {
 };
 
 extern int nfsd_pool_stats_open(struct inode *inode, struct file *file);
+extern int nfsd_pool_stats_release(struct inode *inode, struct file *file);
 
 static struct file_operations pool_stats_operations = {
 	.open		= nfsd_pool_stats_open,
 	.read		= seq_read,
 	.llseek		= seq_lseek,
-	.release	= seq_release,
+	.release	= nfsd_pool_stats_release,
 	.owner		= THIS_MODULE,
 };
 

fs/nfsd/nfssvc.c

@@ -34,6 +34,7 @@
 #include <linux/nfsd/syscall.h>
 #include <linux/lockd/bind.h>
 #include <linux/nfsacl.h>
+#include <linux/seq_file.h>
 
 #define NFSDDBG_FACILITY	NFSDDBG_SVC
 
@@ -614,7 +615,25 @@ nfsd_dispatch(struct svc_rqst *rqstp, __be32 *statp)
 
 int nfsd_pool_stats_open(struct inode *inode, struct file *file)
 {
-	if (nfsd_serv == NULL)
+	int ret;
+	mutex_lock(&nfsd_mutex);
+	if (nfsd_serv == NULL) {
+		mutex_unlock(&nfsd_mutex);
 		return -ENODEV;
-	return svc_pool_stats_open(nfsd_serv, file);
+	}
+	/* bump up the psudo refcount while traversing */
+	svc_get(nfsd_serv);
+	ret = svc_pool_stats_open(nfsd_serv, file);
+	mutex_unlock(&nfsd_mutex);
+	return ret;
+}
+
+int nfsd_pool_stats_release(struct inode *inode, struct file *file)
+{
+	int ret = seq_release(inode, file);
+	mutex_lock(&nfsd_mutex);
+	/* this function really, really should have been called svc_put() */
+	svc_destroy(nfsd_serv);
+	mutex_unlock(&nfsd_mutex);
+	return ret;
 }

net/sunrpc/svc_xprt.c

@@ -1166,11 +1166,6 @@ static void *svc_pool_stats_start(struct seq_file *m, loff_t *pos)
 
 	dprintk("svc_pool_stats_start, *pidx=%u\n", pidx);
 
-	lock_kernel();
-	/* bump up the pseudo refcount while traversing */
-	svc_get(serv);
-	unlock_kernel();
-
 	if (!pidx)
 		return SEQ_START_TOKEN;
 	return (pidx > serv->sv_nrpools ? NULL : &serv->sv_pools[pidx-1]);
@@ -1198,12 +1193,6 @@ static void *svc_pool_stats_next(struct seq_file *m, void *p, loff_t *pos)
 
 static void svc_pool_stats_stop(struct seq_file *m, void *p)
 {
-	struct svc_serv *serv = m->private;
-
-	lock_kernel();
-	/* this function really, really should have been called svc_put() */
-	svc_destroy(serv);
-	unlock_kernel();
 }
 
 static int svc_pool_stats_show(struct seq_file *m, void *p)