Re: Encountered a Null Pointer Problem on the SCSI Layer

Re: Encountered a Null Pointer Problem on the SCSI Layer

[Pete Zaitcev]

> From: Jesper Juhl <jju@dif.dk>
> Date: Tue, 29 Jan 2002 00:57:02 +0100

> > -       if (!dpnt)
> > +       if (!dpnt->device)
> >                 return NULL;    /* No such device */
> 
> Maybe I don't understand this right, but shouldn't that be 
> 
> if (!dpnt || !dpnt->device)
>         return NULL;    /* No such device */

In both cases, the code is like this:

  dpnt = &rscsi_disks[dev_nr];
  if (!dpnt->device)
    return NULL;

So, it is unlikely that dpnt would be zero. It could be if rscsi_disks
were NULL, and in such case whole logics is toast.

-- Pete

RE: Encountered a Null Pointer Problem on the SCSI Layer

[Peter Wong]

Jesper,

     Let's use sd_find_queue() as an example.

     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 depending 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)".

Regards,
Peter

Wai Yee Peter Wong
IBM Linux Technology Center, Performance Analysis
email: wpeter@us.ibm.com



                                                                                                                                       
                      Jesper Juhl                                                                                                      
                      <jju@dif.dk>             To:       "'Pete Zaitcev '" <zaitcev@redhat.com>, Peter Wong/Austin/IBM@IBMUS,          
                                                "'linux-kernel@vger.kernel.org '" <linux-kernel@vger.kernel.org>                       
                      01/28/02 05:57 PM        cc:       "'Jens Axboe '" <axboe@suse.de>                                               
                                               Subject:  RE: Encountered a Null Pointer Problem on the SCSI Layer                      
                                                                                                                                       
                                                                                                                                       
                                                                                                                                       






> -       if (!dpnt)
> +       if (!dpnt->device)
>                 return NULL;    /* No such device */


Maybe I don't understand this right, but shouldn't that be


if (!dpnt || !dpnt->device)
        return NULL;    /* No such device */


?






Best regards,
Jesper Juhl
jju@dif.dk

Re: Encountered a Null Pointer Problem on the SCSI Layer

[Pete Zaitcev]

> --- 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;
>  }

> Wai Yee Peter Wong

There's one more of theese

--- linux-2.4.18-pre1/drivers/scsi/sd.c	Fri Nov  9 14:05:06 2001
+++ linux-2.4.18-pre1-p3/drivers/scsi/sd.c	Mon Jan 28 14:46:11 2002
@@ -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));

-- Pete

Re: Encountered a Null Pointer Problem on the SCSI Layer

[David Ford]

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Might I suggest adding the below instead of swapping it out?

-d

>--- linux-2.4.18-pre1/drivers/scsi/sd.c	Fri Nov  9 14:05:06 2001
>+++ linux-2.4.18-pre1-p3/drivers/scsi/sd.c	Mon Jan 28 14:46:11 2002
>@@ -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));
>


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Re: Encountered a Null Pointer Problem on the SCSI Layer

[Horst von Brand]

Pete Zaitcev <zaitcev@redhat.com> said:
> > --- 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;
> >  }
> 
> > Wai Yee Peter Wong
> 
> There's one more of theese
> 
> --- linux-2.4.18-pre1/drivers/scsi/sd.c	Fri Nov  9 14:05:06 2001
> +++ linux-2.4.18-pre1-p3/drivers/scsi/sd.c	Mon Jan 28 14:46:11 2002
> @@ -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->re
> quest.nr_sectors));

Is is possible for dpnt to be NULL here? Should perhaps be checked...
-- 
Horst von Brand			     http://counter.li.org # 22616

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: wpeter@us.ibm.com