NFSv4: Fix an oops in nfs4_fill_super

The mount statistics patches introduced a call to nfs_free_iostats that is
not only redundant, but actually causes an oops.

Also fix a memory leak due to the lack of a call to nfs_free_iostats on
unmount.
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/inode.c

@@ -281,6 +281,10 @@ nfs_sb_init(struct super_block *sb, rpc_authflavor_t authflavor)
 
 	sb->s_magic      = NFS_SUPER_MAGIC;
 
+	server->io_stats = nfs_alloc_iostats();
+	if (server->io_stats == NULL)
+		return -ENOMEM;
+
 	root_inode = nfs_get_root(sb, &server->fh, &fsinfo);
 	/* Did getting the root inode fail? */
 	if (IS_ERR(root_inode)) {
@@ -294,12 +298,6 @@ nfs_sb_init(struct super_block *sb, rpc_authflavor_t authflavor)
 	}
 	sb->s_root->d_op = server->rpc_ops->dentry_ops;
 
-	server->io_stats = nfs_alloc_iostats();
-	if (!server->io_stats) {
-		no_root_error = -ENOMEM;
-		goto out_no_root;
-	}
-
 	/* mount time stamp, in seconds */
 	server->mount_time = jiffies;
 
@@ -1822,6 +1820,7 @@ static void nfs_kill_super(struct super_block *s)
 
 	rpciod_down();		/* release rpciod */
 
+	nfs_free_iostats(server->io_stats);
 	kfree(server->hostname);
 	kfree(server);
 }
@@ -2122,7 +2121,6 @@ static struct super_block *nfs4_get_sb(struct file_system_type *fs_type,
 out_free:
 	kfree(server->mnt_path);
 	kfree(server->hostname);
-	nfs_free_iostats(server->io_stats);
 	kfree(server);
 	return s;
 }
@@ -2143,6 +2141,7 @@ static void nfs4_kill_super(struct super_block *sb)
 
 	rpciod_down();
 
+	nfs_free_iostats(server->io_stats);
 	kfree(server->hostname);
 	kfree(server);
 }

fs/nfs/iostat.h

@@ -156,7 +156,8 @@ static inline struct nfs_iostats *nfs_alloc_iostats(void)
 
 static inline void nfs_free_iostats(struct nfs_iostats *stats)
 {
-	free_percpu(stats);
+	if (stats != NULL)
+		free_percpu(stats);
 }
 
 #endif