On Wed, 2007-10-31 at 11:58 -0400, Alan Stern wrote: > On Wed, 31 Oct 2007, James Bottomley wrote: > > > On Wed, 2007-10-31 at 07:32 -0700, Greg KH wrote: > > > Hm, I seem to have missed the part in this thread where someone said > > > that it was valid to have a parent reference a child device. That's > > > just wrong and needs to be fixed. Is that in the scsi layer somewhere? > > > The block layer? It sure isn't in the driver core... > > > > This is the piece I'm still not clear on. It's something to do with the > > gendisk. I'd have to look in block, but I believe the queue takes a ref > > to the gendisk. > > > > The scsi_device has a ref to the queue and the scsi_disk (in sd) has a > > ref to both the scsi_device and the gendisk. That means, until sd is > > unbound and the scsi_disk released, there's an implied unbreakable > > reference chain. > > > > at least, I think that's what the problem is. > > No, you haven't got it right. > > Parent Child Grandchild > ------ ----- ---------- > scsi_device gendisk request_queue This is what I think doesn't happen. The scsi_device should never be parented to the gendisk. > > The odd part is that the scsi_device holds a reference to the queue. > That creates a reference loop: > > scsi_device holds ref to request_queue (done explicitly) > request_queue holds ref to gendisk (implicit, parent-child) agreed. > gendisk holds ref to scsi_device (implicit, parent-child) Where exactly does this last part happen? the scsi_device is a mid layer object; the mid-layer doesn't know about gendisks. James - To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
