[PATCH]drivers/ata/libata-eh.c:1509 unneeded memset()

[René Bolldorf]

We don't need this ;-).

Best regards Ren� Bolldorf & a happy new year in advance.

--- ./drivers/ata/libata-eh.c 2009-12-30 23:44:05.578988545 +0100
+++ ./drivers/ata/libata-eh.c 2009-12-30 23:45:06.991987607 +0100
@@ -1505,9 +1505,6 @@ static unsigned int atapi_eh_request_sen

DPRINTK("ATAPI request sense\n");

- /* FIXME: is this needed? */
- memset(sense_buf, 0, SCSI_SENSE_BUFFERSIZE);
-
/* initialize sense_buf with the error register,
* for the case where they are -not- overwritten
*/
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[Jeff Garzik]

On 12/30/2009 05:59 PM, Ren� Bolldorf wrote:
> We don't need this ;-).
>
> Best regards Ren� Bolldorf & a happy new year in advance.
>
> --- ./drivers/ata/libata-eh.c 2009-12-30 23:44:05.578988545 +0100
> +++ ./drivers/ata/libata-eh.c 2009-12-30 23:45:06.991987607 +0100
> @@ -1505,9 +1505,6 @@ static unsigned int atapi_eh_request_sen
>
> DPRINTK("ATAPI request sense\n");
>
> - /* FIXME: is this needed? */
> - memset(sense_buf, 0, SCSI_SENSE_BUFFERSIZE);

I need a little bit more detail than an unqualified statement... Did
you audit all paths leading to this code point?

Jeff

[René Bolldorf]

On 01/07/10 20:15, Jeff Garzik wrote:
> I need a little bit more detail than an unqualified statement... Did
> you audit all paths leading to this code point?

Yes, and my two systems running fine with the patch, no oops or panic's.

[Rolf Eike Beer]

Ren� Bolldorf wrote:

> On 01/07/10 21:34, Ren� Bolldorf wrote:
> > On 01/07/10 20:15, Jeff Garzik wrote:
> >> I need a little bit more detail than an unqualified statement... Did
> >> you audit all paths leading to this code point?
> >
> > Yes, and my two systems running fine with the patch, no oops or panic's.
>

> Sry forgot that:

> /* initialize sense_buf with the error register,
> * for the case where they are -not- overwritten
> */

> sense_buf[0] = 0x70;
> sense_buf[2] = dfl_sense_key;
>
> So i think memset() is not needed and works very well without it.

What happens to sense_buf[1]?

[James Bottomley]

On Thu, 2010-01-07 at 14:15 -0500, Jeff Garzik wrote:

> On 12/30/2009 05:59 PM, René Bolldorf wrote:
> > We don't need this ;-).
> >

> > Best regards René Bolldorf & a happy new year in advance.

> >
> > --- ./drivers/ata/libata-eh.c 2009-12-30 23:44:05.578988545 +0100
> > +++ ./drivers/ata/libata-eh.c 2009-12-30 23:45:06.991987607 +0100
> > @@ -1505,9 +1505,6 @@ static unsigned int atapi_eh_request_sen
> >
> > DPRINTK("ATAPI request sense\n");
> >
> > - /* FIXME: is this needed? */
> > - memset(sense_buf, 0, SCSI_SENSE_BUFFERSIZE);
>
> I need a little bit more detail than an unqualified statement... Did
> you audit all paths leading to this code point?

There are two code paths coming into here. One directly from the scsi
sense buffer:

if (!(qc->ap->pflags & ATA_PFLAG_FROZEN)) {
tmp = atapi_eh_request_sense(qc->dev,
qc->scsicmd->sense_buffer,
qc->result_tf.feature >> 4);

Which is fine because SCSI zeros the sense buffer.

But one also here:

u8 *sense_buffer = dev->link->ap->sector_buf;
[...]
err_mask = atapi_eh_request_sense(dev, sense_buffer, sense_key);

Which doesn't look OK because it looks like the sector_buf isn't cleared
(and it is reused).

James

[René Bolldorf]

On 01/08/10 16:28, James Bottomley wrote:
> On Thu, 2010-01-07 at 14:15 -0500, Jeff Garzik wrote:
>> On 12/30/2009 05:59 PM, René Bolldorf wrote:
>>> We don't need this ;-).
>>>

>>> Best regards René Bolldorf& a happy new year in advance.

>>>
>>> --- ./drivers/ata/libata-eh.c 2009-12-30 23:44:05.578988545 +0100
>>> +++ ./drivers/ata/libata-eh.c 2009-12-30 23:45:06.991987607 +0100
>>> @@ -1505,9 +1505,6 @@ static unsigned int atapi_eh_request_sen
>>>
>>> DPRINTK("ATAPI request sense\n");
>>>
>>> - /* FIXME: is this needed? */
>>> - memset(sense_buf, 0, SCSI_SENSE_BUFFERSIZE);
>>
>> I need a little bit more detail than an unqualified statement... Did
>> you audit all paths leading to this code point?
>
> There are two code paths coming into here. One directly from the scsi
> sense buffer:
>

> if (!(qc->ap->pflags& ATA_PFLAG_FROZEN)) {

> tmp = atapi_eh_request_sense(qc->dev,
> qc->scsicmd->sense_buffer,
> qc->result_tf.feature>> 4);
>
> Which is fine because SCSI zeros the sense buffer.
>
> But one also here:
>
> u8 *sense_buffer = dev->link->ap->sector_buf;
> [...]
> err_mask = atapi_eh_request_sense(dev, sense_buffer, sense_key);
>
> Which doesn't look OK because it looks like the sector_buf isn't cleared
> (and it is reused).
>
> James
>
>

Thank's, you're right. I have overseen this, sry for that.

[Marc Bejarano]

and once more in plain text. �(sorry vger)

2010/1/11 Marc Bejarano <be...@beej.org>:
> oops. �seems that GMANE's reply function only goes to a single "newsgroup".
> �original recipients re-added.
> marc
> ----
> From: Marc Bejarano <beej <at> beej.org>
> Subject:�Re: [PATCH]drivers/ata/libata-eh.c:1509 unneeded memset()
> Newsgroups:�gmane.linux.scsi
> Date: 2010-01-08 22:21:09 GMT (2 days, 20 hours and 40 minutes ago)

>
> Ren� Bolldorf <xsecute <at> googlemail.com> writes:
>> On 01/08/10 16:28, James Bottomley wrote:
>> > On Thu, 2010-01-07 at 14:15 -0500, Jeff Garzik wrote:

>> >> On 12/30/2009 05:59 PM, Ren� Bolldorf wrote:
>> >>> We don't need this .

>
>> >>> - /* FIXME: is this needed? */
>> >>> - memset(sense_buf, 0, SCSI_SENSE_BUFFERSIZE);
>> >>
>> >> I need a little bit more detail than an unqualified statement... �Did
>> >> you audit all paths leading to this code point?
>

>> > But one also here:
>> >
>> > u8 *sense_buffer = dev->link->ap->sector_buf;
>> > [...]
>> > err_mask = atapi_eh_request_sense(dev, sense_buffer, sense_key);
>> >
>> > Which doesn't look OK because it looks like the sector_buf isn't cleared
>> > (and it is reused).
>> >
>> > James
>> >
>> >
>>
>> Thank's, you're right. I have overseen this, sry for that.
>

> Ren�: perhaps you'd like to submit a patch that substitutes FIXME comment
> for one that explains why the memset is needed, crediting James in the
> description? �we may as well gain something permanent from this discussion
> that you started :)
>
> cheers,
> marc
>
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>

> ----

[René Bolldorf]

I hope that's good enough explained :-).

Best regards
Ren�

--- ./drivers/ata/libata-eh.c 2010-01-07 23:21:23.622464012 +0100
+++ ./drivers/ata/libata-eh.c 2010-01-11 21:11:19.869092897 +0100
@@ -1505,7 +1505,10 @@ static unsigned int atapi_eh_request_sen

DPRINTK("ATAPI request sense\n");

- /* FIXME: is this needed? */
+ /* make sure sense_buf is cleared then atapi_eh_request_sense is
called.
+ * (to make sure nothing get's reused.)
+ * thanks to James Bottomley
+ */
memset(sense_buf, 0, SCSI_SENSE_BUFFERSIZE);

/* initialize sense_buf with the error register,

[Marc Bejarano]

2010/1/11 Ren� Bolldorf <xse...@googlemail.com>:

> I hope that's good enough explained :-).

definitely an improvement, but i think jeff is going to want your
S-O-B and at least a patch title, if no description :)

> + � � � /* make sure sense_buf is cleared then atapi_eh_request_sense is
> called.

s/then/when/ ?

> + � � � �* (to make sure nothing get's reused.)

probably not necessary

> + � � � �* thanks to James Bottomley

this may be better in a patch description

cheers,
marc
--