diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c
index eb5a755..cd6bb9a 100644
--- a/fs/quota/dquot.c
+++ b/fs/quota/dquot.c
@@ -2164,7 +2164,9 @@
 	struct dentry *dentry;
 	int error;
 
+	mutex_lock(&sb->s_root->d_inode->i_mutex);
 	dentry = lookup_one_len(qf_name, sb->s_root, strlen(qf_name));
+	mutex_unlock(&sb->s_root->d_inode->i_mutex);
 	if (IS_ERR(dentry))
 		return PTR_ERR(dentry);