Messages in this thread | | | Date | Mon, 24 Mar 2008 10:58:44 -0700 | From | Greg KH <> | Subject | Re: Fixing the main programmer thinko with the device model |
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On Mon, Mar 24, 2008 at 10:39:48AM -0500, James Bottomley wrote: > Having just spent the weekend tracking two separate driver model > problems through SCSI, I believe the biggest trap everyone falls into > with the driver model (well, OK, at least with SCSI) is to try to defer > a callback to the device ->release routine without realising that > somewhere along the callback path we're going to drop a reference to the > device. > > You can do this very inadvertently: One developer didn't realise > bsg_unregister_queue() released a ref, and another didn't realise that > transport_destroy_device() held one. > > The real problem is that it's fantastically easy to do this ... it's not > at all clear which of the cleanup routines actually release references > unless you dig down into them and it's very difficult to detect because > all that happens is that devices don't get released when they should, > which isn't something we ever warn about.
Sounds like a documentation issue for how the scsi layer is using the driver model more than anything else. None of the other busses seem to have these kinds of issues that I can see, is it just because of your complex usage model?
> So, what I was wondering is: is there any way we can reliably detect > and warn when someone does this.
Warn that a device did not get released when the programmer thought it should yet they forgot to call the correct function to have that happen? That seems a bit difficult :)
Also note that the scsi layer usage of multiple refcounted objects within the same structure might be causing some of these issues, that's a bug in how the scsi layer has implmented things much more so than how the driver core is implemented, right?
thanks,
greg k-h
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