[v3.7 Regression] [SCSI] sd: Implement support for WRITE SAME

[Joseph Salisbury]

Hi Martin,

A bug was opened against the Ubuntu kernel[0].  After a kernel bisect, 
it was found that reverting the following commit resolved this bug:

commit 5db44863b6ebbb400c5e61d56ebe8f21ef48b1bd
Author: Martin K. Petersen <martin.petersen at oracle.com>
Date:   Tue Sep 18 12:19:32 2012 -0400
[SCSI] sd: Implement support for WRITE SAME

The regression was introduced as of v3.7-rc7.

The bug can be reproduced with the following commands, which will 
operate on a virtual scsi_debug device, so they won't change any data on 
the test system. However, this will completely crash the system:

sudo modprobe scsi_debug
sudo luksformat -t ext4 /dev/sdb <- Or whatever device gets assigned 
after inserting scsi_debug.
sudo cryptsetup luksOpen /dev/sdb treasure

Everything works fine up to here, but the following will cause the crash:

sudo mount /dev/mapper/treasure /mnt

The bug can be reproduced on bare metal, in a VM and on i386 or amd64.

I see that you are the author of this patch, so I wanted to run this by 
you.  I was thinking of requesting a revert for v3.7, but I wanted to 
get your feedback first.


Thanks,

Joe


[0] https://bugs.launchpad.net/bugs/1089818