On Wed, 7 Nov 2007, Hannes Reinecke wrote:
> Alan Stern wrote:
> >
> > Thus we have a cycle:
> >
> > 1&2: request_queue isn't released before scsi_device;
> >
> > 3: scsi_device isn't released before gendisk;
> >
> > 4: gendisk isn't released before request_queue.
> >
> > The dependency in 1&2 is hard-coded into the SCSI core. If I
> > understand correctly, the core really does need the request_queue to
> > hang around as long as the scsi_device is still present. According to
> > James Bottomley, any block device driver should be expected to have a
> > similar requirement.
> >
> This is actually true, but as other block device drivers create the
> LUN (or the equivalent thereof), the request queue, and the block device
> at the same time or under control of the driver itself they don't have
> this problem.
> It's only due to the decoupling of the block driver from the underlying
> device (ie sd driver and scsi_device) when this problem arises.
I don't understand your reasoning. If the same parent-child
relationships exist then it doesn't matter who creates the data
stuctures. All that matters is that the block device's reference to
the request_queue isn't dropped until the device is released.
> > But the dependencies in 3 and 4 are unnecessary. They are artifacts,
> > caused by the fact that a kobject doesn't drop its reference to its
> > parent until it is released. If instead the reference to the parent
> > were dropped when the kobject was removed then 3 and 4 wouldn't apply.
> >
> And should be okay as the device isn't accessible from userland
> anyway after doing a device_del(). And the implication is that it's
> going to be remove soon entirely. So we're just moving the timing
> of the eventual call to the ->release() function; the events will
> be triggered by device_del() and won't be changed.
> And if some device actually requires a reference to the parent
> during ->release() it can as well acquire it manually and shouldn't
> rely on the core logic to do that automatically.
My thinking exactly.
Alan Stern
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