libata sg chaining support fix

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

drivers/ata/libata-core.c

@@ -4952,16 +4952,18 @@ static void __atapi_pio_bytes(struct ata_queued_cmd *qc, unsigned int bytes)
 {
 	int do_write = (qc->tf.flags & ATA_TFLAG_WRITE);
 	struct scatterlist *sg = qc->__sg;
+	struct scatterlist *lsg = sg_last(qc->__sg, qc->n_elem);
 	struct ata_port *ap = qc->ap;
 	struct page *page;
 	unsigned char *buf;
 	unsigned int offset, count;
+	int no_more_sg = 0;
 
 	if (qc->curbytes + bytes >= qc->nbytes)
 		ap->hsm_task_state = HSM_ST_LAST;
 
 next_sg:
-	if (unlikely(qc->cursg == sg_last(qc->__sg, qc->n_elem))) {
+	if (unlikely(no_more_sg)) {
 		/*
 		 * The end of qc->sg is reached and the device expects
 		 * more data to transfer. In order not to overrun qc->sg
@@ -5023,6 +5025,9 @@ next_sg:
 	qc->cursg_ofs += count;
 
 	if (qc->cursg_ofs == sg->length) {
+		if (qc->cursg == lsg)
+			no_more_sg = 1;
+
 		qc->cursg = sg_next(qc->cursg);
 		qc->cursg_ofs = 0;
 	}