On Wed, 31 Oct 2007, James Bottomley wrote:
> > Yes, the queue is a child of the disk.
>
> Right, so this goes gendisk->queue (-> meaning parent of, or takes
> reference to)
No, no! The _child_ takes an implicit reference to the _parent_, not
the other way around.
> > > The scsi_device has a ref to the queue
> >
> > Yeah, while the queue is a grandchild of the scsi_device with the
> > unified sysfs layout.
>
> No, the scsi_device is a direct parent of the queue, so we have
>
> scsi_device->queue
Wrong -- the gendisk is the direct parent of the queue. The relevant
line is in ll_rw_blk.c:blk_register_queue():
q->kobj.parent = kobject_get(&disk->dev.kobj);
> > Yes, sounds right. We need to break that deleted-but-wait-for-cleanup at
> > least at one of the devices involved.
>
> But it's broken when the driver is unbound. Diagrammatically it's:
>
> scsi_disk -> scsi_device -> queue
> -> gendisk ->
>
> It's not circular, it's released when scsi_disk is released. It can
> become circular if there's some hidden dependency between any of the
> components ... but I don't think there is.
Forget about the scsi_disk. It isn't part of the problem. Just
concentrate on the scsi_device, the gendisk, and the queue. We have:
scsi_device <- gendisk <- queue <- scsi_device,
where "A <- B" means that B holds a reference to A.
Alan Stern
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