[Bug 16058] [BUG] Cannot boot any kernel from 2.6.27 on if a 256 byte sector SCSI disk is attached

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https://bugzilla.kernel.org/show_bug.cgi?id=16058





--- Comment #4 from Alan Stern <stern@rowland.harvard.edu>  2010-05-28 14:58:55 ---
On Fri, 28 May 2010, Mark Hounschell wrote:

> First READ(10):
> 
>  sde:
> ahc_calc_residual: Entered
> ahc_calc_residual: return Case 5-1 resid = 0x800
> ahc_calc_residual: return Case 5-2 resid = 0x800
> 
> scsi_finish_command: Entered for cmd(10):0x28 0x00 0x00 0x00 0x00 0x00
> 0x00 0x00 0x08 0x00
> cmd->result = 0x00000000
> good_bytes == old_good_bytes = 0x800  scsi_get_resid(cmd) = 0x800
> New good_bytes = 0x0
> scsi_finish_command: Complete
> 
> From here it just keeps repeating this read of 8 blocks. (2048 bytes) so
> it looks like the machine is hung.

Probably not hung, just doing a lot of retries.  It should time out 
eventually, but it might take a long time (perhaps as long as 15 
minutes).  The combination of the block layer and the SCSI layer isn't 
very good at knowing when to give up.

> Now, I know for a fact that _if_ this read CDB is actually being sent to
> the drive, it's actual residual count will be zero. These are working
> disks and that read CDB is valid.
> 
> Why is ahc_calc_residual saying that the residual count is as though the
> read never took place? I noticed that the first read on all the SATA
> drives was for 4096 bytes, why is this one only 2048? Should it have
> been 4096 and ahc_calc_residual assume that?

I don't know the answer to any of these questions.  They could well be
due to bugs in the driver, and I know nothing about how the aic7xxx
driver works.  You should talk to someone who does.

In the meantime, you can track this down a little farther by adding
printk's to the appropriate places in drivers/scsi/sd.c.  Look at
sd_prep_fn() to see why there's 2048 bytes instead of 4096.

Alan Stern

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