linux-kernel - Re: Subtle but oops causing problem with class

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Message-Id: <1217354790.6103.36.camel@localhost.localdomain>
Date:	Tue, 29 Jul 2008 13:06:30 -0500
From:	James Bottomley <James.Bottomley@...senPartnership.com>
To:	Kay Sievers <kay.sievers@...y.org>
Cc:	Hannes Reinecke <hare@...e.de>,
	linux-scsi <linux-scsi@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: Subtle but oops causing problem with class_device->device
	conversion

On Tue, 2008-07-29 at 19:59 +0200, Kay Sievers wrote:
> On Tue, 2008-07-29 at 12:42 -0500, James Bottomley wrote:
> > It's taken me a while to track this down.  Basically there's an oops in
> > scsi_transport_spi that's directly caused by this.
> > 
> > What happened is that you made all class devices become real devices and
> > be parented to devices they were formerly allied to through the class
> > device dev pointer.  This means that effectively you expanded the child
> > list of every device to include not only its real children but also its
> > class devices.
> > 
> > This breaks in device_for_each_child *if* the routine in the iterator
> > doesn't perform checks on the devices it gets back (scsi_transport_spi
> > was assuming that every device it got was embedded in a struct
> > scsi_device because they're the only logical children of a scsi_target).
> > 
> > I can fix the SCSI breakage, but the whole tree will need auditing to
> > check that nothing else is using this assumption.
> 
> I guess it's caused by:
>   [SCSI] add scsi_host and scsi_target to scsi_bus
> 
>   This patch implements scsi_host and scsi_target device types
>   and adds both to the scsi_bus.
>   http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=b0ed43360fdca227048d88a08290365cb681c1a8
> 
> and not by the re-parenting, so it should be limited to SCSI, right?

No .. read the email.  It's caused by adding extra children to the
device via the class_device conversion.  device_for_each_child doesn't
care what the type is (although that might be a potential generic fix
for this).

So, it's definitely not confined to SCSI.

James


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