Messages in this thread Patch in this message | | | Date | Tue, 19 Feb 2002 00:01:39 +0100 | From | Stephan von Krawczynski <> | Subject | Re: [PATCH] Encountered a Null Pointer Problem on the SCSI Layer |
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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.
Are you 100% sure, that there is no case where dpnt==NULL? Because if there is such a possibility, your patch will blow up. It would be completely safe to check both
(!dpnt && !dpnt->device)
Regards, Stephan
> > 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 > > - > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ > - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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