s390/pci: Allow re-add of a reserved but not yet removed device

The architecture assumes that PCI functions can be removed synchronously
as PCI events are processed. This however clashes with the reference
counting of struct pci_dev which allows device drivers to hold on to a
struct pci_dev reference even as the underlying device is removed. To
bridge this gap commit 2a671f77ee49 ("s390/pci: fix use after free of
zpci_dev") keeps the struct zpci_dev in ZPCI_FN_STATE_RESERVED state
until common code releases the struct pci_dev. Only when all references
are dropped, the struct zpci_dev can be removed and freed.

Later commit a46044a92add ("s390/pci: fix zpci_zdev_put() on reserve")
moved the deletion of the struct zpci_dev from the zpci_list in
zpci_release_device() to the point where the device is reserved. This
was done to prevent handling events for a device that is already being
removed, e.g. when the platform generates both PCI event codes 0x304
and 0x308. In retrospect, deletion from the zpci_list in the release
function without holding the zpci_list_lock was also racy.

A side effect of this handling is that if the underlying device
re-appears while the struct zpci_dev is in the ZPCI_FN_STATE_RESERVED
state, the new and old instances of the struct zpci_dev and/or struct
pci_dev may clash. For example when trying to create the IOMMU sysfs
files for the new instance. In this case, re-adding the new instance is
aborted. The old instance is removed, and the device will remain absent
until the platform issues another event.

Fix this by allowing the struct zpci_dev to be brought back up right
until it is finally removed. To this end also keep the struct zpci_dev
in the zpci_list until it is finally released when all references have
been dropped.

Deletion from the zpci_list from within the release function is made
safe by using kref_put_lock() with the zpci_list_lock. This ensures that
the releasing code holds the last reference.

Cc: stable@vger.kernel.org
Fixes: a46044a92add ("s390/pci: fix zpci_zdev_put() on reserve")
Reviewed-by: Gerd Bayer <gbayer@linux.ibm.com>
Tested-by: Gerd Bayer <gbayer@linux.ibm.com>
Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

0 files changed, 0 insertions, 0 deletions