cifs_rqst_page_to_kvec(struct smb_rqst *rqst, unsigned int idx,
			struct kvec *iov)
{
	/*
	 * FIXME: We could avoid this kmap altogether if we used
	 * kernel_sendpage instead of kernel_sendmsg. That will only
	 * work if signing is disabled though as sendpage inlines the
	 * page directly into the fraglist. If userspace modifies the
	 * page after we calculate the signature, then the server will
	 * reject it and may break the connection. kernel_sendmsg does
	 * an extra copy of the data and avoids that issue.
	 */
	iov->iov_base = kmap(rqst->rq_pages[idx]);

	/* if last page, don't send beyond this offset into page */
	if (idx == (rqst->rq_npages - 1))
		iov->iov_len = rqst->rq_tailsz;
	else
		iov->iov_len = rqst->rq_pagesz;
}

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.