Messages in this thread Patch in this message | | | Subject | [PATCH] Encountered a Null Pointer Problem on the SCSI Layer | From | "Peter Wong" <> | Date | Mon, 18 Feb 2002 15:03:05 -0600 |
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A while ago, I reported that 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. After my patch was sent out, Pete Zaitcev of Red Hat identified a similar problem in sd_init_command of the same file.
Let's consider sd_find_queue().
If the array pointed by rscsi_disk has been allocated, dpnt cannot be null.
If rscsi_disk has NOT been allocated, dpnt = &rscsi_disks[target] may NOT be null, and it depends on the value of target. Thus, "if (!dpnt)" is not sufficient anyway.
You can also look at sd_attach(), in which "if (!dpnt->device)" is tested, not "if (!dpnt)".
Please check.
The following patch is based on the 2.4.18-pre7 code: --------------------------------------------------------------------------- --- linux/drivers/scsi/sd.c Mon Feb 18 13:36:42 2002 +++ linux-2.4.17-diskio/drivers/scsi/sd.c Mon Feb 18 13:29:34 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; } @@ -302,7 +302,7 @@
dpnt = &rscsi_disks[dev]; if (devm >= (sd_template.dev_max << 4) || - !dpnt || + !dpnt->device || !dpnt->device->online || block + SCpnt->request.nr_sectors > sd[devm].nr_sects) { SCSI_LOG_HLQUEUE(2, printk("Finishing %ld sectors\n", SCpnt->request.nr_sectors)); --------------------------------------------------------------------------- Regards, Peter
Wai Yee Peter Wong IBM Linux Technology Center, Performance Analysis email: wpeter@us.ibm.com
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