cxl: use pcibios_free_controller_deferred() when removing vPHBs

When cxl removes a vPHB, it's possible that the pci_controller may be freed
before all references to the devices on the vPHB have been released. This
in turn causes an invalid memory access when the devices are eventually
released, as pcibios_release_device() attempts to call the phb's
release_device hook.

In cxl_pci_vphb_remove(), remove the existing call to
pcibios_free_controller(). Instead, use
pcibios_free_controller_deferred() to free the pci_controller after all
devices have been released. Export pci_set_host_bridge_release() so we can
do this.

Cc: stable@vger.kernel.org
Signed-off-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com>
Reviewed-by: Matthew R. Ochs <mrochs@linux.vnet.ibm.com>
Acked-by: Ian Munsie <imunsie@au1.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

drivers/misc/cxl/vphb.c

@@ -230,6 +230,11 @@ int cxl_pci_vphb_add(struct cxl_afu *afu)
 	if (phb->bus == NULL)
 		return -ENXIO;
 
+	/* Set release hook on root bus */
+	pci_set_host_bridge_release(to_pci_host_bridge(phb->bus->bridge),
+				    pcibios_free_controller_deferred,
+				    (void *) phb);
+
 	/* Claim resources. This might need some rework as well depending
 	 * whether we are doing probe-only or not, like assigning unassigned
 	 * resources etc...
@@ -256,7 +261,10 @@ void cxl_pci_vphb_remove(struct cxl_afu *afu)
 	afu->phb = NULL;
 
 	pci_remove_root_bus(phb->bus);
-	pcibios_free_controller(phb);
+	/*
+	 * We don't free phb here - that's handled by
+	 * pcibios_free_controller_deferred()
+	 */
 }
 
 static bool _cxl_pci_is_vphb_device(struct pci_controller *phb)

drivers/pci/host-bridge.c

@@ -44,6 +44,7 @@ void pci_set_host_bridge_release(struct pci_host_bridge *bridge,
 	bridge->release_fn = release_fn;
 	bridge->release_data = release_data;
 }
+EXPORT_SYMBOL_GPL(pci_set_host_bridge_release);
 
 void pcibios_resource_to_bus(struct pci_bus *bus, struct pci_bus_region *region,
 			     struct resource *res)