Re: [patch] scsi: revert "[SCSI] Get rid of scsi_cmnd->done"

James Bottomley
2008-01-06T13:58:18Z

On Sun, 2008-01-06 at 03:55 +0100, Peter Osterlund wrote:
> Linus Torvalds <torvalds@linux-foundation.org> writes:
>
> > On Wed, 2 Jan 2008, James Bottomley wrote:
> >
> > > Look at the taxonomy of the bug. This is the form of the error:
> > >
> > > buffer I/O error on device sr0, logical block 20304
> > > attempt to access beyond end of device
> > > sr0: rw=0, want=81224, limit=40944
> > >
> > > The last limit is the most suggestive, that comes straight from
> > > bdev->bd_inode->i_size>>9 and is supposed to be the size of the block
> > > device in 512 byte blocks. For a 4.7GB DVD, it's a little small.
> > > Nothing in the sr code sets this directly (although it does come from
> > > get_blkdev() for the first opener). pktcdvd does set it, though ... and
> > > probably wrongly if the drive in question isn't UDF formatted.
>
> pktcdvd sets it when opening the /dev/pktcdvd device, but when the
> drive is later opened as /dev/scd0, there is nothing that sets it
> back. (Btw, 40944 is possible if the disk is a CDRW that was formatted
> with "cdrwtool -m 10236".)
>
> The problem is that pktcdvd opens the cd device in non-blocking mode
> when pktsetup is run, and doesn't close it again until pktsetup -d
> is run. The effect is that if you meanwhile open the cd device,
> blkdev.c:do_open() doesn't call bd_set_size() because bdev->bd_openers
> is non-zero.
>
> I don't know the correct way to fix this. Maybe adding bd_set_size()
> to sr.c:get_sectorsize() which already does set_capacity() would
> work.

Could be ... this is deep viro magic, though; I've added him to the Cc
list to get his input.

> > .. but you're ignoring the fact that if pktcdvd sets it wrong, then it
> > should be visible with the pre-commit kernel *also*.
>
> I can repeat this bug, both with and without the scsi patch that is
> claimed to make a difference, both with an external USB drive and an
> internal IDE drive.
>
> To repeat:
>
> 1. Start with an empty drive.
> 2. pktsetup 0 /dev/scd0
> 3. Insert a CD containing an isofs filesystem.
> 4. mount /dev/pktcdvd/0 /mnt/tmp
> 5. umount /mnt/tmp
> 6. Press the eject button.
> 7. Insert a DVD containing a non-writable filesystem.
> 8. mount /dev/scd0 /mnt/tmp
> 9. find /mnt/tmp -type f -print0 | xargs -0 sha1sum >/dev/null
> 10. If the DVD contains data beyond the physical size of a CD, you
> get I/O errors in the terminal, and dmesg reports lots of
> "attempt to access beyond end of device" errors.

Brilliant! I can confirm the reproduction of the bug too (that's with
the originally fingered commit reverted).

James