Encountered a Null Pointer Problem on the SCSI Layer

[Peter Wong]

I encountered a null pointer problem on the SCSI layer when
I was testing Mingming Cao's diskio patch "diskio-stat-rq-2414"
on 2.4.14.

Mingming's patch is at http://sourceforge.net/projects/lse/.

The code in sd_find_queue() that protects against accessing a
non-existent device is not correct. The patch to fix it is given
below. Please check.

The following patch is based on the 2.4.18-pre7 code:

---------------------------------------------------------------------------
--- linux/drivers/scsi/sd.c     Fri Jan 25 14:01:07 2002
+++ linux-2.4.17-diskio/drivers/scsi/sd.c       Fri Jan 25 13:57:01 2002
@@ -279,7 +279,7 @@
        target = DEVICE_NR(dev);

        dpnt = &rscsi_disks[target];
-       if (!dpnt)
+       if (!dpnt->device)
                return NULL;    /* No such device */
        return &dpnt->device->request_queue;
 }
---------------------------------------------------------------------------

Regards,
Peter

Wai Yee Peter Wong
IBM Linux Technology Center, Performance Analysis
email: [e-mail]