When we hot-remove a device, usually the host sends us a PCI_EJECT message,
and a PCI_BUS_RELATIONS message with bus_rel->device_count == 0.
When we execute the quick hot-add/hot-remove test, the host may not send
us the PCI_EJECT message if the guest has not fully finished the
initialization by sending the PCI_RESOURCES_ASSIGNED* message to the
host, so it's potentially unsafe to only depend on the
pci_destroy_slot() in hv_eject_device_work() because the code path
create_root_hv_pci_bus()
-> hv_pci_assign_slots()
is not called in this case. Note: in this case, the host still sends the
guest a PCI_BUS_RELATIONS message with bus_rel->device_count == 0.
In the quick hot-add/hot-remove test, we can have such a race before
the code path
pci_devices_present_work()
-> new_pcichild_device()
adds the new device into the hbus->children list, we may have already
received the PCI_EJECT message, and since the tasklet handler
hv_pci_onchannelcallback()
may fail to find the "hpdev" by calling
get_pcichild_wslot(hbus, dev_message->wslot.slot)
hv_pci_eject_device() is not called; Later, by continuing execution
create_root_hv_pci_bus()
-> hv_pci_assign_slots()
creates the slot and the PCI_BUS_RELATIONS message with
bus_rel->device_count == 0 removes the device from hbus->children, and
we end up being unable to remove the slot in
hv_pci_remove()
-> hv_pci_remove_slots()
Remove the slot in pci_devices_present_work() when the device
is removed to address this race.
pci_devices_present_work() and hv_eject_device_work() run in the
singled-threaded hbus->wq, so there is not a double-remove issue for the
slot.
We cannot offload hv_pci_eject_device() from hv_pci_onchannelcallback()
to the workqueue, because we need the hv_pci_onchannelcallback()
synchronously call hv_pci_eject_device() to poll the channel
ringbuffer to work around the "hangs in hv_compose_msi_msg()" issue
fixed in commit de0aa7b2f9 ("PCI: hv: Fix 2 hang issues in
hv_compose_msi_msg()")
Fixes: a15f2c08c7 ("PCI: hv: support reporting serial number as slot information")
Signed-off-by: Dexuan Cui <decui@microsoft.com>
[lorenzo.pieralisi@arm.com: rewritten commit log]
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Stephen Hemminger <stephen@networkplumber.org>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Cc: stable@vger.kernel.org
340d455699