[libata] fix bugs in ATAPI padding DMA mapping code
The ATAPI pad-to-next-32bit-boundary code modifies the scatterlist's
length variable, sometimes to zero. x86-64 platform would oops if a
zero-length scatterlist entry was asked to be mapped. Work around this
by ensuring that we never DMA-map a zero length buffer or SG entry.
diff --git a/drivers/scsi/libata-core.c b/drivers/scsi/libata-core.c
index d81db3a..1ccaf46 100644
--- a/drivers/scsi/libata-core.c
+++ b/drivers/scsi/libata-core.c
@@ -2409,7 +2409,8 @@
pad_buf = ap->pad + (qc->tag * ATA_DMA_PAD_SZ);
if (qc->flags & ATA_QCFLAG_SG) {
- dma_unmap_sg(ap->host_set->dev, sg, qc->n_elem, dir);
+ if (qc->n_elem)
+ dma_unmap_sg(ap->host_set->dev, sg, qc->n_elem, dir);
/* restore last sg */
sg[qc->orig_n_elem - 1].length += qc->pad_len;
if (pad_buf) {
@@ -2419,8 +2420,10 @@
kunmap_atomic(psg->page, KM_IRQ0);
}
} else {
- dma_unmap_single(ap->host_set->dev, sg_dma_address(&sg[0]),
- sg_dma_len(&sg[0]), dir);
+ if (sg_dma_len(&sg[0]) > 0)
+ dma_unmap_single(ap->host_set->dev,
+ sg_dma_address(&sg[0]), sg_dma_len(&sg[0]),
+ dir);
/* restore sg */
sg->length += qc->pad_len;
if (pad_buf)
@@ -2619,6 +2622,11 @@
sg->length, qc->pad_len);
}
+ if (!sg->length) {
+ sg_dma_address(sg) = 0;
+ goto skip_map;
+ }
+
dma_address = dma_map_single(ap->host_set->dev, qc->buf_virt,
sg->length, dir);
if (dma_mapping_error(dma_address)) {
@@ -2628,6 +2636,7 @@
}
sg_dma_address(sg) = dma_address;
+skip_map:
sg_dma_len(sg) = sg->length;
DPRINTK("mapped buffer of %d bytes for %s\n", sg_dma_len(sg),
@@ -2655,7 +2664,7 @@
struct ata_port *ap = qc->ap;
struct scatterlist *sg = qc->__sg;
struct scatterlist *lsg = &sg[qc->n_elem - 1];
- int n_elem, dir;
+ int n_elem, pre_n_elem, dir, trim_sg = 0;
VPRINTK("ENTER, ata%u\n", ap->id);
assert(qc->flags & ATA_QCFLAG_SG);
@@ -2689,13 +2698,24 @@
sg_dma_len(psg) = ATA_DMA_PAD_SZ;
/* trim last sg */
lsg->length -= qc->pad_len;
+ if (lsg->length == 0)
+ trim_sg = 1;
DPRINTK("padding done, sg[%d].length=%u pad_len=%u\n",
qc->n_elem - 1, lsg->length, qc->pad_len);
}
+ pre_n_elem = qc->n_elem;
+ if (trim_sg && pre_n_elem)
+ pre_n_elem--;
+
+ if (!pre_n_elem) {
+ n_elem = 0;
+ goto skip_map;
+ }
+
dir = qc->dma_dir;
- n_elem = dma_map_sg(ap->host_set->dev, sg, qc->n_elem, dir);
+ n_elem = dma_map_sg(ap->host_set->dev, sg, pre_n_elem, dir);
if (n_elem < 1) {
/* restore last sg */
lsg->length += qc->pad_len;
@@ -2704,6 +2724,7 @@
DPRINTK("%d sg elements mapped\n", n_elem);
+skip_map:
qc->n_elem = n_elem;
return 0;