Re: Patch "sd: Disable support for 256 byte/sector disks" has been added to the 4.0-stable tree

[James Bottomley <James.Bottomley@HansenPartnership.com>]

On Wed, 2015-06-03 at 13:37 +0000, James Bottomley wrote:
> On Wed, 2015-06-03 at 11:29 +0200, Jiri Slaby wrote:
> > On 06/03/2015, 08:35 AM, gregkh@linuxfoundation.org wrote:
> > > From 74856fbf441929918c49ff262ace9835048e4e6a Mon Sep 17 00:00:00 2001
> > > From: Mark Hounschell <dmarkh@cfl.rr.com>
> > > Date: Wed, 13 May 2015 10:49:09 +0200
> > > Subject: sd: Disable support for 256 byte/sector disks
> > > 
> > > From: Mark Hounschell <dmarkh@cfl.rr.com>
> > > 
> > > commit 74856fbf441929918c49ff262ace9835048e4e6a upstream.
> > > 
> > > 256 bytes per sector support has been broken since 2.6.X,
> > > and no-one stepped up to fix this.
> > > So disable support for it.
> > > 
> > > Signed-off-by: Mark Hounschell <dmarkh@cfl.rr.com>
> > > Signed-off-by: Hannes Reinecke <hare@suse.de>
> > > Signed-off-by: James Bottomley <JBottomley@Odin.com>
> > > Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > > 
> > > ---
> > >  drivers/scsi/sd.c |   19 +++++--------------
> > >  1 file changed, 5 insertions(+), 14 deletions(-)
> > > 
> > > --- a/drivers/scsi/sd.c
> > > +++ b/drivers/scsi/sd.c
> > > @@ -1624,6 +1624,7 @@ static unsigned int sd_completed_bytes(s
> > >  {
> > >  	u64 start_lba = blk_rq_pos(scmd->request);
> > >  	u64 end_lba = blk_rq_pos(scmd->request) + (scsi_bufflen(scmd) / 512);
> > > +	u64 factor = scmd->device->sector_size / 512;
> > >  	u64 bad_lba;
> > >  	int info_valid;
> > >  	/*
> > > @@ -1645,16 +1646,9 @@ static unsigned int sd_completed_bytes(s
> > >  	if (scsi_bufflen(scmd) <= scmd->device->sector_size)
> > >  		return 0;
> > >  
> > > -	if (scmd->device->sector_size < 512) {
> > > -		/* only legitimate sector_size here is 256 */
> > > -		start_lba <<= 1;
> > > -		end_lba <<= 1;
> > > -	} else {
> > > -		/* be careful ... don't want any overflows */
> > > -		unsigned int factor = scmd->device->sector_size / 512;
> > > -		do_div(start_lba, factor);
> > > -		do_div(end_lba, factor);
> > > -	}
> > 
> > Hmm, you do 'unsigned int' -> 'u64' switch of factor type here. But this
> > commit:
> > commit ef80d1e18b014af08741cf688e3fdda1fb71363f
> > Author: Geert Uytterhoeven <geert@linux-m68k.org>
> > Date:   Mon Nov 4 10:21:05 2013 +0100
> > 
> >     [SCSI] sd: Do not call do_div() with a 64-bit divisor
> > 
> > did the switch in the opposite direction deliberately.
> > 
> > So why did you do the change, given sector_size is uint?
> 
> Primarily because no-one spotted the reversal and none of the static
> checkers warns about it.
> 
> This is the trivial fix, but we should do something about the checkers.

Actually, I think there's no problem: all the architectures now have the
correct conversion of the base argument.

Author: Andreas Schwab <schwab@linux-m68k.org>
Date:   Fri Aug 9 15:14:08 2013 +0200

    m68k: Truncate base in do_div()

Fixed this in m68k, which was the last one, so it looks like there's no
issue and ef80d1e18b014af08741cf688e3fdda1fb71363f was pointless.

James