Hi Bjorn,

Doing additional testing for a distribution backport of commit
05703271c3cd ("PCI/IOV: Add PCI rescan-remove locking when
enabling/disabling SR-IOV") Benjamin found a hang with s390's
recover attribute. Further investigation showed this to be a deadlock by
recursively trying to take pci_rescan_remove lock when removing a PF
with enabled SR-IOV.

The issue can be reproduced on both s390 and x86_64 with:

    $ echo <NUM> > /sys/bus/pci/devices/<pf>/sriov_numvfs
    $ echo 1 > /sys/bus/pci/devices/<pf>/remove

As this seems worse than the original, hard to hit, race fixed by the
cited commit I think we first want to revert the broken fix.

Following that patch 2 attempts to fix the original issue by taking the
PCI rescan/remove lock directly before calling into the driver's
sriov_configure() callback enforcing the rule that this should only
be called with the pci_rescan_remove_lock held.

Thanks,
Niklas

Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
---
Changes in v3:
- Rebased on v6.19-rc1, also verified issue is still there and the fix
  still works
- Added more of the lockdep splat for better context
- Link to v2: https://lore.kernel.org/r/20251119-revert_sriov_lock-v2-0-ea50eb1e8f96@linux.ibm.com

Changes in v2:
- Collected R-b from Benjamin
- Link to v1: https://lore.kernel.org/r/20251030-revert_sriov_lock-v1-0-70f82ade426f@linux.ibm.com

---
Niklas Schnelle (2):
      Revert "PCI/IOV: Add PCI rescan-remove locking when enabling/disabling SR-IOV"
      PCI/IOV: Fix race between SR-IOV enable/disable and hotplug

 drivers/pci/iov.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)
---
base-commit: 8f0b4cce4481fb22653697cced8d0d04027cb1e8
change-id: 20251029-revert_sriov_lock-aef4557f360f

Best regards,
-- 
Niklas Schnelle