static inline pmd_t pmd_read_atomic(pmd_t *pmdp)
{
	pmdval_t ret;
	u32 *tmp = (u32 *)pmdp;

	ret = (pmdval_t) (*tmp);
	if (ret) {
		/*
		 * If the low part is null, we must not read the high part
		 * or we can end up with a partial pmd.
		 */
		smp_rmb();
		ret |= ((pmdval_t)*(tmp + 1)) << 32;
	}

	return (pmd_t) { ret };
}
The program contains a code sequence that can run concurrently with other code, and the code sequence 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 that is operating concurrently.