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:   Tue, 14 Jul 2020 16:03:14 -0700
From:   James Bottomley <jejb@...ux.ibm.com>
To:     Lee Jones <lee.jones@...aro.org>
Cc:     Hannes Reinecke <hare@...e.de>, 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 Tue, 2020-07-14 at 22:39 +0100, 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.

Well, we have what looks like a fix now.  The reason it matters is that
 if the bus is not in AHD_MODE_SCSI when the routine is called, it ends
up being in a wrong state when the routine exits, so you abort one
command and screw up another.  Ultimately I bet escalation to bus reset
fixes it, so everything appears to work, but it might have worked a lot
better if the original mode were restored.

This is error handling code, so most installations run just fine
without ever invoking it.

James