linux-kernel - Re: [BUG] unable to handle kernel paging request in next-20080516

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Date:	Fri, 23 May 2008 20:34:25 +0100
From:	Sitsofe Wheeler <sitsofe@...oo.com>
To:	linux-kernel@...r.kernel.org
Cc:	linux-scsi@...r.kernel.org
Subject:  Re: [BUG] unable to handle kernel paging request in next-20080516

<posted & mailed>

James Bottomley wrote:

> Actually, I think this is a very subtle bug; what I think is happening
> is that after Hannes sysfs changes, we now add scsi_bus_type to the
> target device.  However, scsi_bus_uevent() unconditionally casts from
> dev to a struct scsi_device and then looks at the type entry.  My theory
> is that in this particular config going from struct scsi_target to
> struct device and back to struct scsi_device actually tips us over into
> unmapped space for the -> type deref.
> 
> Hopefully this should fix it by checking the device type before doing
> the deref.

This fixed the problem for me (it was horribly intermittant but I've done
10+ consecutive reboots without seeing an oopos). I changed the patch to
printk everytime the condition was hit and it seems to happen twice per
PATA device - once after each scsi?: pata_via message and then again after
each scsi 0:0:0:0: Direct-Accesss ATA DISKID etc : 0 ANSI: 5 .

The thing I don't understand about your explanation is that it sounds like
the device struct is being round-tripped (but is just being cast to
different things along the way). If this is the case why would this problem
ever arise? Surely if it is really a struct scsi_device underneath there
should be no problem?

-- 
Sitsofe | http://sucs.org/~sits/

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