struct dentry *d_add_ci(struct dentry *dentry, struct inode *inode,
			struct qstr *name)
{
	struct dentry *found, *res;

	/*
	 * First check if a dentry matching the name already exists,
	 * if not go ahead and create it now.
	 */
	found = d_hash_and_lookup(dentry->d_parent, name);
	if (found) {
		iput(inode);
		return found;
	}
	if (d_in_lookup(dentry)) {
		found = d_alloc_parallel(dentry->d_parent, name,
					dentry->d_wait);
		if (IS_ERR(found) || !d_in_lookup(found)) {
			iput(inode);
			return found;
		}
	} else {
		found = d_alloc(dentry->d_parent, name);
		if (!found) {
			iput(inode);
			return ERR_PTR(-ENOMEM);
		} 
	}
	res = d_splice_alias(inode, found);
	if (res) {
		dput(found);
		return res;
	}
	return found;
}

The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.