Hello, I've reported the bug port-xen/45158, and I've spotted the error, but I'm not sure if the fix is correct. The problem is that xbdback tries to attach an already attached device and it fails at VOP_OPEN (which seems normal), but at detach time the kernel panics with the error described on the bug report when trying to detach the device. The attached patch prevents xbdback from trying to attach an already attached device, but maybe the problem is with bdevsw_lookup, bdevvp, vn_lock or VOP_OPEN and the fix is just a workaround that prevents this functions from executing. Regards, Roger.
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