linux-kernel - Re: [PATCH v2 24/24] scsi: aic7xxx: aic79xx_osm: Remove set but unused variabes 'saved_scsiid' and 'saved

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Date:   Wed, 15 Jul 2020 07:58:37 +0200
From:   Hannes Reinecke <hare@...e.de>
To:     Lee Jones <lee.jones@...aro.org>,
        James Bottomley <jejb@...ux.ibm.com>
Cc:     martin.petersen@...cle.com, linux-kernel@...r.kernel.org,
        linux-scsi@...r.kernel.org, Hannes Reinecke <hare@...e.com>
Subject: Re: [PATCH v2 24/24] scsi: aic7xxx: aic79xx_osm: Remove set but
 unused variabes 'saved_scsiid' and 'saved_modes'

On 7/14/20 11:39 PM, Lee Jones wrote:
> On Tue, 14 Jul 2020, James Bottomley wrote:
> 
>> On Tue, 2020-07-14 at 09:46 +0200, Hannes Reinecke wrote:
>>> On 7/13/20 10:00 AM, Lee Jones wrote:
>>>> Haven't been used since 2006.
>>>>
>>>> Fixes the following W=1 kernel build warning(s):
>>>>
>>>>   drivers/scsi/aic7xxx/aic79xx_osm.c: In function
>>>> ‘ahd_linux_queue_abort_cmd’:
>>>>   drivers/scsi/aic7xxx/aic79xx_osm.c:2155:17: warning: variable
>>>> ‘saved_modes’ set but not used [-Wunused-but-set-variable]
>>>>   drivers/scsi/aic7xxx/aic79xx_osm.c:2148:9: warning: variable
>>>> ‘saved_scsiid’ set but not used [-Wunused-but-set-variable]
>>>>
>>>> Cc: Hannes Reinecke <hare@...e.com>
>>>> Signed-off-by: Lee Jones <lee.jones@...aro.org>
>>>> ---
>>>>   drivers/scsi/aic7xxx/aic79xx_osm.c | 4 ----
>>>>   1 file changed, 4 deletions(-)
>>>>
>>>> diff --git a/drivers/scsi/aic7xxx/aic79xx_osm.c
>>>> b/drivers/scsi/aic7xxx/aic79xx_osm.c
>>>> index 3782a20d58885..140c4e74ddd7e 100644
>>>> --- a/drivers/scsi/aic7xxx/aic79xx_osm.c
>>>> +++ b/drivers/scsi/aic7xxx/aic79xx_osm.c
>>>> @@ -2141,14 +2141,12 @@ ahd_linux_queue_abort_cmd(struct scsi_cmnd
>>>> *cmd)
>>>>   	u_int  saved_scbptr;
>>>>   	u_int  active_scbptr;
>>>>   	u_int  last_phase;
>>>> -	u_int  saved_scsiid;
>>>>   	u_int  cdb_byte;
>>>>   	int    retval;
>>>>   	int    was_paused;
>>>>   	int    paused;
>>>>   	int    wait;
>>>>   	int    disconnected;
>>>> -	ahd_mode_state saved_modes;
>>>>   	unsigned long flags;
>>>>   
>>>>   	pending_scb = NULL;
>>>> @@ -2239,7 +2237,6 @@ ahd_linux_queue_abort_cmd(struct scsi_cmnd
>>>> *cmd)
>>>>   		goto done;
>>>>   	}
>>>>   
>>>> -	saved_modes = ahd_save_modes(ahd);
>>>>   	ahd_set_modes(ahd, AHD_MODE_SCSI, AHD_MODE_SCSI);
>>>>   	last_phase = ahd_inb(ahd, LASTPHASE);
>>>>   	saved_scbptr = ahd_get_scbptr(ahd);
>>>> @@ -2257,7 +2254,6 @@ ahd_linux_queue_abort_cmd(struct scsi_cmnd
>>>> *cmd)
>>>>   	 * passed in command.  That command is currently active on
>>>> the
>>>>   	 * bus or is in the disconnected state.
>>>>   	 */
>>>> -	saved_scsiid = ahd_inb(ahd, SAVED_SCSIID);
>>>>   	if (last_phase != P_BUSFREE
>>>>   	    && SCB_GET_TAG(pending_scb) == active_scbptr) {
>>>>   
>>>>
>>>
>>> Reviewed-by: Hannes Reinecke <hare@...e.de>
>>
>> Hey, you don't get to do that ... I asked you to figure out why we're
>> missing an ahd_restore_modes().  Removing the ahd_save_modes() is
>> cosmetic: it gets rid of a warning but doesn't fix the problem.  I'd
>> rather keep the warning until the problem is fixed and the problem is
>> we need a mode save/restore around the ahd_set_modes() which is only
>> partially implemented in this function.
> 
> I had a look.  Traced it back to the dawn of time (time == Git), then
> delved even further back by downloading and trawling through ~10-15
> tarballs.  It looks as though drivers/scsi/aic7xxx/aic79xx_osm.c was
> upstreamed in v2.5.60, nearly 20 years ago.  'saved_modes' has been
> unused since at least then.  If no one has complained in 2 decades,
> I'd say it probably isn't an issue worth perusing.
> 
That's not really the point; this function is the first stage of error 
recovery. And the only real way of exercising this is to inject a 
command timeout, which is nearly impossible without dedicated hardware.
So this function will have a very limited exposure, but nevertheless a 
quite crucial function.
Hence I'm not quite agree with your reasoning, and rather would have it 
fixed.
But as we're having an alternative fix now, it might be best if you 
could drop it from your patchset and we'll fix it separately.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke            Teamlead Storage & Networking
hare@...e.de                               +49 911 74053 688
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