On Mon, Aug 20, 2018 at 12:10:59PM +1000, Benjamin Herrenschmidt wrote: > I chose to create a new mutex which we should be able to address other > similar races if we find them. The other solutions that I dismissed > were: > > - Using the device_lock. A explained previously, this is tricky, I > prefer not using this for anything other than locking against > concurrent add/remove. The main issue is that drivers will be sometimes > called in context where that's already held, so we can't take it inside > pci_enable_device() and I'd rather not add new constraints such as > "pci_enable_device() must be only called from probe() unless you also > take the device lock". It would be tricky to audit everybody... > > - Using a global mutex. We could move the bridge lock from AER to core > code for example, and use that. But it doesn't buy us much, and > slightly redecuces parallelism. It also makes it a little bit more > messy to walk up the bridge chain, we'd have to do a > pci_enable_device_unlocked or something, messy. +1 from my side for adding a struct mutex to struct pci_dev to protect state changes. The device_lock() primarily protects binding / unbinding of the device and pci_dev state may have to be changed while binding / unbinding. A global lock invites deadlocks if multiple devices are added / removed concurrently where one is a parent of the other. (Think hot-removal of multiple devices on a Thunderbolt daisy-chain.) As said I'd also welcome folding PCI_DEV_DISCONNECTED into enum pci_channel_state, either as an additional state or by using pci_channel_io_perm_failure. Thanks, Lukas
