SFQ_EMPTY_SLOT
WRITE_ONCE(q->ht[slot->hash], SFQ_EMPTY_SLOT);
if (x == SFQ_EMPTY_SLOT) {
WRITE_ONCE(q->ht[slot->hash], SFQ_EMPTY_SLOT);
WRITE_ONCE(q->ht[slot->hash], SFQ_EMPTY_SLOT);
if (x == SFQ_EMPTY_SLOT) {
q->ht[i] = SFQ_EMPTY_SLOT;
if (idx != SFQ_EMPTY_SLOT) {
if (READ_ONCE(q->ht[i]) == SFQ_EMPTY_SLOT) {