pci: question about the life cycle of pci_dev and its parent pci_bus

Hi,

I have a question about the life cycle of pci_dev and its parent pci_bus.
In pci_destroy_dev(), we remove the pci_dev from the bus_list, so
pci_dev is isolated from its parent pci_bus, and their life cycle are
independent too. But it seems that in pci_dev, we can still access the
pci_bus from the pointer pci_dev->bus.  To resolve such issue, I think
during the pci_dev removal,  there should be process to 1.prevent the
reader incoming 2. ensure the current reader has exit.  But can not
find them.

Could anyone tell me?

Thanx, pingfan