static unsigned long get_seg_limit(struct pt_regs *regs, int seg_reg_idx)
{
	struct desc_struct desc;
	unsigned long limit;
	short sel;

	sel = get_segment_selector(regs, seg_reg_idx);
	if (sel < 0)
		return 0;

	if (user_64bit_mode(regs) || v8086_mode(regs))
		return -1L;

	if (!sel)
		return 0;

	if (!get_desc(&desc, sel))
		return 0;

	/*
	 * If the granularity bit is set, the limit is given in multiples
	 * of 4096. This also means that the 12 least significant bits are
	 * not tested when checking the segment limits. In practice,
	 * this means that the segment ends in (limit << 12) + 0xfff.
	 */
	limit = get_desc_limit(&desc);
	if (desc.g)
		limit = (limit << 12) + 0xfff;

	return limit;
}
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.