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SubjectRe: 2.4.21-pre3 kernel crash
On Tue, Jan 28 2003, Larry Sendlosky wrote:
> I was glad to see the physical page support in 2.4.20.
> (and also noticed that the current BK tree clobbered it
> on a patch set from Alan).
>
> One question,
>
> + lastdataend = bh_phys(bh) + bh->b_size;
>
> bh_phys(x) uses bh->b_page. Does it make a difference
> if bh->b_page is zero? What if someone combines virt and phys
> buffer addresses in bh list?

Yes good catch! New version attached.

===== drivers/ide/ide-dma.c 1.7 vs edited =====
--- 1.7/drivers/ide/ide-dma.c Wed Nov 20 18:46:24 2002
+++ edited/drivers/ide/ide-dma.c Tue Jan 28 23:04:32 2003
@@ -249,6 +249,7 @@
{
struct buffer_head *bh;
struct scatterlist *sg = hwif->sg_table;
+ unsigned long lastdataend = ~0UL;
int nents = 0;

if (hwif->sg_dma_active)
@@ -256,24 +257,42 @@

bh = rq->bh;
do {
- unsigned char *virt_addr = bh->b_data;
- unsigned int size = bh->b_size;
+ int contig = 0;
+
+ if (bh->b_page) {
+ if (bh_phys(bh) == lastdataend)
+ contig = 1;
+ } else {
+ if ((unsigned long) bh->b_data == lastdataend)
+ contig = 1;
+ }
+
+ if (contig) {
+ sg[nents - 1].length += bh->b_size;
+ lastdataend += bh->b_size;
+ continue;
+ }

if (nents >= PRD_ENTRIES)
return 0;

- while ((bh = bh->b_reqnext) != NULL) {
- if ((virt_addr + size) != (unsigned char *) bh->b_data)
- break;
- size += bh->b_size;
- }
memset(&sg[nents], 0, sizeof(*sg));
- sg[nents].address = virt_addr;
- sg[nents].length = size;
- if(size == 0)
- BUG();
+
+ if (bh->b_page) {
+ sg[nents].page = bh->b_page;
+ sg[nents].offset = bh_offset(bh);
+ lastdataend = bh_phys(bh) + bh->b_size;
+ } else {
+ if ((unsigned long) bh->b_data < PAGE_SIZE)
+ BUG();
+
+ sg[nents].address = bh->b_data;
+ lastdataend = (unsigned long) bh->b_data + bh->b_size;
+ }
+
+ sg[nents].length = bh->b_size;
nents++;
- } while (bh != NULL);
+ } while ((bh = bh->b_reqnext) != NULL);

if(nents == 0)
BUG();
--
Jens Axboe

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