One instance per net-ns.  There's a fixed subset (several files in root,
an optional symlink in root + initially empty /clients/) + per-client
subdirectory in /clients/.  Clients can appear only after the filesystem
is there and they are all gone before it gets through ->kill_sb().

Fixed subset created in fill_super(), regular files by simple_fill_super(),
then a subdirectory and a symlink - manually.  It is removed by
kill_litter_super().

Per-client subdirectories are created by nfsd_client_mkdir() (populated
with client-supplied list of files in them).  Removed by nfsd_client_rmdir(),
which is simple_recursive_removal().

All dentries except for the ones from simple_fill_super() come from
	* nfsd_mkdir() (subdirectory, dentry from simple_start_creating()).
	  Called from fill_super() (creates initially empty /clients)
	  and from nfsd_client_mkdir (creates a per-client subdirectory
	  in /clients).
	* _nfsd_symlink() (symlink, dentry from simple_start_creating()), called
	  from fill_super().
	* nfsdfs_create_files() (regulars, dentry from simple_start_creating()),
	  called only from nfsd_client_mkdir().

Turn d_instatiate() + inode_unlock() into d_make_persistent() + simple_done_creating()
in nfsd_mkdir(), _nfsd_symlink() and nfsdfs_create_files() and we are done.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
 fs/nfsd/nfsctl.c | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
index 2b79129703d5..5ce9a49e76ba 100644
--- a/fs/nfsd/nfsctl.c
+++ b/fs/nfsd/nfsctl.c

@@ -1137,11 +1137,11 @@ static struct dentry *nfsd_mkdir(struct dentry *parent, struct nfsdfs_client *nc
 		inode->i_private = ncl;
 		kref_get(&ncl->cl_ref);
 	}
-	d_instantiate(dentry, inode);
+	d_make_persistent(dentry, inode);
 	inc_nlink(dir);
 	fsnotify_mkdir(dir, dentry);
-	inode_unlock(dir);
-	return dentry;
+	simple_done_creating(dentry);
+	return dentry;	// borrowed
 }
 
 #if IS_ENABLED(CONFIG_SUNRPC_GSS)

@@ -1170,9 +1170,9 @@ static void _nfsd_symlink(struct dentry *parent, const char *name,
 	inode->i_link = (char *)content;
 	inode->i_size = strlen(content);
 
-	d_instantiate(dentry, inode);
+	d_make_persistent(dentry, inode);
 	fsnotify_create(dir, dentry);
-	inode_unlock(dir);
+	simple_done_creating(dentry);
 }
 #else
 static inline void _nfsd_symlink(struct dentry *parent, const char *name,

@@ -1228,11 +1228,11 @@ static int nfsdfs_create_files(struct dentry *root,
 		kref_get(&ncl->cl_ref);
 		inode->i_fop = files->ops;
 		inode->i_private = ncl;
-		d_instantiate(dentry, inode);
+		d_make_persistent(dentry, inode);
 		fsnotify_create(dir, dentry);
 		if (fdentries)
-			fdentries[i] = dentry;
-		inode_unlock(dir);
+			fdentries[i] = dentry; // borrowed
+		simple_done_creating(dentry);
 	}
 	return 0;
 }

@@ -1346,7 +1346,7 @@ static void nfsd_umount(struct super_block *sb)
 
 	nfsd_shutdown_threads(net);
 
-	kill_litter_super(sb);
+	kill_anon_super(sb);
 	put_net(net);
 }
 

-- 
2.47.3