Messages in this thread | | | Date | Fri, 24 Feb 2023 05:19:18 +0100 | From | Lukas Wunner <> | Subject | Re: [PATCH RESEND] PCI: s390: Fix use-after-free of PCI bus resources with s390 per-function hotplug |
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On Thu, Feb 23, 2023 at 01:53:45PM -0600, Bjorn Helgaas wrote: > Hmm. Good question. Off the top of my head, I can't explain the > difference between pci_rescan_remove_lock and pci_bus_sem, so I'm > confused, too. I added Lukas in case he has a ready explanation.
pci_bus_sem is a global lock which protects the "devices" list of all pci_bus structs.
We do have a bunch of places left where the "devices" list is accessed without holding pci_bus_sem, though I've tried to slowly eliminate them.
pci_rescan_remove_lock is a global "big kernel lock" which serializes any device addition and removal.
pci_rescan_remove_lock is known to be far too course-grained and thus deadlock-prone, particularly if hotplug ports are nested (as is the case with Thunderbolt). It needs to be split up into several smaller locks which protect e.g. allocation of resources of a bus (bus numbers or MMIO / IO space) and whatever else needs to be protected. It's just that nobody has gotten around to identify what exactly needs to be protected, adding the new locks and removing pci_rescan_remove_lock.
Thanks,
Lukas
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