On Wed, Oct 02, 2024 at 04:39:37PM -0700, Davidlohr Bueso wrote: > > + set_bit(PCI_DEV_ADDED, &dev->priv_flags); > > +} > > So set_bit does not imply any barriers. Huh. Hannes told me the same thing just last weak, and I was thinking "nah, it's an atomic operation." But I'm mistaken thinking that provides a memory barrier. > Does this matter in the future when breaking up > pci_rescan_remove_lock? For example, what prevents things like: We're still far from being able to remove the big pci rescan/remove lock, but yes, that's the idea. This should be safe as-is since it is still using that lock, I can add smp barriers to make the memroy dependencies explicit. > pci_bus_add_device() pci_stop_dev() > pci_dev_assign_added() > dev->priv_flags [S] > pci_dev_test_and_clear_added() // true > dev->priv_flags [L] > device_attach(&dev->dev) > device_release_driver(&dev->dev) > > ... I guess that implied barrier from that device_lock() in device_attach(). > I am not familiar with this code, but overall I think any locking rework should > explain more about the ordering implications in the changes if the end result Oh, goot point. This sequence shouldn't be possible with either the existing or proposed bus locking, and I can certainly add more detailed explanations.
