Public bug reported:
Description: s390/pci: Fix immediate re-add of PCI function after
remove
Symptom: A PCI function may be reserved directly after being
deconfigured. If it subsequently returns back in the standby
state Linux may not be able to use the new instance generating
a kernel warning about trying to create an already existing
sysfs file for the IOMMU.
Problem: The problem occurs because the new instance of the same
underlying device is created before the prior instance is
completely torn down. This happens because the lifetime of the
PCI device representation in Linux is determined by reference
counts. A driver, the network stack, or even user-space
(including via vfio-pci) may be holding onto the device
represenation even after the underlying device is gone.
Solution: The solution to this is twofold. Firstly allow re-using the
pre-existing struct zpci_dev and/or struct pci_dev for the newly
re-added instance of the underlying device up until the point
where the struct zpci_dev is fully removed. Secondly serialize
the addition and removal of PCI functions such that re-adding
a new instance, after the old one is already being removed, will
wait for the removal to finish before adding the new instance.
This fix also builds on prior upstream work of serializing state
transitions for PCI devices e.g. from configured to standby.
Reproduction: This problem was originally found with firmware which
temporarily reserves NETH PCI functions to check for pending
service when the last FID of a PCHID is deconfigured. When
nothing is pending the PCI function is immediately returned in
the standby state, thus triggering this issue quite reliably.
Upstream-ID: 0d48566d4b58946c8e1b0baac0347616060a81c9
bcb5d6c769039c8358a2359e7c3ea5d97ce93108
6ee600bfbe0f818ffb7748d99e9b0c89d0d9f02a
c4a585e952ca403a370586d3f16e8331a7564901
42420c50c68f3e95e90de2479464f420602229fc
05a2538f2b48500cf4e8a0a0ce76623cc5bafcf1
d76f9633296785343d45f85199f4138cb724b6d2
47c397844869ad0e6738afb5879c7492f4691122
4b1815a52d7eb03b3e0e6742c6728bc16a4b2d1d
774a1fa880bc949d88b5ddec9494a13be733dfa8
** Affects: linux (Ubuntu)
Importance: Undecided
Assignee: Skipper Bug Screeners (skipper-screen-team)
Status: New
** Tags: architecture-s39064 bugnameltc-213761 severity-high
targetmilestone-inin---
** Tags added: architecture-s39064 bugnameltc-213761 severity-high
targetmilestone-inin---
** Changed in: ubuntu
Assignee: (unassigned) => Skipper Bug Screeners (skipper-screen-team)
** Package changed: ubuntu => linux (Ubuntu)
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https://bugs.launchpad.net/bugs/2114174
Title:
[UBUNTU 24.04] s390/pci: Fix immediate re-add of PCI function after
remove
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