linux-kernel - Re: BUG in: Driver core: convert block from raw kobjects to core devices

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Message-ID: <Pine.LNX.4.44L0.0710241354560.29002-100000@netrider.rowland.org>
Date:	Wed, 24 Oct 2007 14:01:06 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Kay Sievers <kay.sievers@...y.org>
cc:	Greg KH <greg@...ah.com>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	Hannes Reinecke <hare@...e.de>
Subject: Re: BUG in: Driver core: convert block from raw kobjects to core
 devices

On Tue, 23 Oct 2007, Kay Sievers wrote:

> > Yes; I haven't been able to figure out why we get different results.
> > 
> > > There must be something going wrong with the block patch in conjunction
> > > with the crazy SCSI release logic.

I found out why it works on my system -- which still leaves open the 
question of why it fails on yours.

Although the gendisk device is a child of the scsi_device, nevertheless 
disk->kobj is not a child of the scsi_device's embedded kobject.  
Instead it is a child of the static (!) block_depr kobject, which is 
defined in block/genhd.c.  Hence the disk's single reference to the 
scsi_device is indeed dropped when the disk is unregistered, which 
breaks the loop of circular references.

It works this way because I have CONFIG_SYSFS_DEPRECATED set; perhaps
you don't.  If you compare the two versions of get_device_parent() in
drivers/base/core.c you'll see the difference (it's the dev_type ==
&disk_type case).

Alan Stern

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