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SubjectRe: CDROM troubles
On Sun, May 06 2001, Phil Stracchino wrote:
> On Sun, May 06, 2001 at 03:05:00AM -0700, Phil Stracchino wrote:
> > Hey folks,
> > I'm seeing a problem with mounting CDs using a Toshiba XM-6401TA CDROM
> > drive attached to an Adaptec AHA1542CF controller (scsi1) on kernel 2.4.3
> > and 2.4.4. The behavior seems to be fairly consistent as follows:
> >
> > first mount and unmount works normally, no unusual events logged
> > second mount and unmount works normally, no unusual events logged
> > third mount locks up the machine. looks like a kernel panic.
> >
> > Any ideas?
>
>
> Panic is confirmed. This time, it lived long enough to log:
>
> May 6 14:05:05 babylon5 kernel: Kernel panic: scsi_free:Bad offset
>
> Since it involves the CDROM, the aha1542 driver is implicated. Why it's
> getting a bad offset, I don't understand enough about the SCSI drivers to
> know; all the scsi_free calls in aha1542.c look identical to me.
>
> Would any Linux SCSI gurus care to let me know any diagnostic procedures
> recommended for nailing this one?

The panic should be fixed with attached patch.

--
Jens Axboe

diff -urN --exclude-from /home/axboe/cdrom/exclude /opt/kernel/linux-2.4.4-pre2/drivers/scsi/sr.c linux/drivers/scsi/sr.c
--- /opt/kernel/linux-2.4.4-pre2/drivers/scsi/sr.c Mon Feb 19 19:25:17 2001
+++ linux/drivers/scsi/sr.c Mon Apr 9 09:18:46 2001
@@ -262,7 +262,7 @@
static int sr_scatter_pad(Scsi_Cmnd *SCpnt, int s_size)
{
struct scatterlist *sg, *old_sg = NULL;
- int i, fsize, bsize, sg_ent;
+ int i, fsize, bsize, sg_ent, sg_count;
char *front, *back;

back = front = NULL;
@@ -290,17 +290,24 @@
/*
* extend or allocate new scatter-gather table
*/
- if (SCpnt->use_sg)
+ sg_count = SCpnt->use_sg;
+ if (sg_count)
old_sg = (struct scatterlist *) SCpnt->request_buffer;
else {
- SCpnt->use_sg = 1;
+ sg_count = 1;
sg_ent++;
}

- SCpnt->sglist_len = ((sg_ent * sizeof(struct scatterlist)) + 511) & ~511;
- if ((sg = scsi_malloc(SCpnt->sglist_len)) == NULL)
+ i = ((sg_ent * sizeof(struct scatterlist)) + 511) & ~511;
+ if ((sg = scsi_malloc(i)) == NULL)
goto no_mem;

+ /*
+ * no more failing memory allocs possible, we can safely assign
+ * SCpnt values now
+ */
+ SCpnt->sglist_len = i;
+ SCpnt->use_sg = sg_count;
memset(sg, 0, SCpnt->sglist_len);

i = 0;
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