NFS: Ensure that rmdir() waits for sillyrenames to complete

If an NFS client does

	mkdir("dir");
	fd = open("dir/file");
	unlink("dir/file");
	close(fd);
	rmdir("dir");

then the asynchronous nature of the sillyrename operation means that
we can end up getting EBUSY for the rmdir() in the above test. Fix
that by ensuring that we wait for any in-progress sillyrenames
before sending the rmdir() to the server.
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/dir.c

@@ -1694,12 +1694,19 @@ int nfs_rmdir(struct inode *dir, struct dentry *dentry)
 			dir->i_sb->s_id, dir->i_ino, dentry->d_name.name);
 
 	trace_nfs_rmdir_enter(dir, dentry);
-	error = NFS_PROTO(dir)->rmdir(dir, &dentry->d_name);
-	/* Ensure the VFS deletes this inode */
-	if (error == 0 && dentry->d_inode != NULL)
-		clear_nlink(dentry->d_inode);
-	else if (error == -ENOENT)
-		nfs_dentry_handle_enoent(dentry);
+	if (dentry->d_inode) {
+		nfs_wait_on_sillyrename(dentry);
+		error = NFS_PROTO(dir)->rmdir(dir, &dentry->d_name);
+		/* Ensure the VFS deletes this inode */
+		switch (error) {
+		case 0:
+			clear_nlink(dentry->d_inode);
+			break;
+		case -ENOENT:
+			nfs_dentry_handle_enoent(dentry);
+		}
+	} else
+		error = NFS_PROTO(dir)->rmdir(dir, &dentry->d_name);
 	trace_nfs_rmdir_exit(dir, dentry, error);
 
 	return error;

fs/nfs/unlink.c

@@ -207,6 +207,13 @@ static int nfs_call_unlink(struct dentry *dentry, struct nfs_unlinkdata *data)
 	return ret;
 }
 
+void nfs_wait_on_sillyrename(struct dentry *dentry)
+{
+	struct nfs_inode *nfsi = NFS_I(dentry->d_inode);
+
+	wait_event(nfsi->waitqueue, atomic_read(&nfsi->silly_count) <= 1);
+}
+
 void nfs_block_sillyrename(struct dentry *dentry)
 {
 	struct nfs_inode *nfsi = NFS_I(dentry->d_inode);

include/linux/nfs_fs.h

@@ -524,6 +524,7 @@ static inline void nfs4_label_free(void *label) {}
  * linux/fs/nfs/unlink.c
  */
 extern void nfs_complete_unlink(struct dentry *dentry, struct inode *);
+extern void nfs_wait_on_sillyrename(struct dentry *dentry);
 extern void nfs_block_sillyrename(struct dentry *dentry);
 extern void nfs_unblock_sillyrename(struct dentry *dentry);
 extern int  nfs_sillyrename(struct inode *dir, struct dentry *dentry);