PCI: Protect pci_reassign_bridge_resources() against concurrent addition/removal

pci_reassign_bridge_resources() can be called by pci_resize_resource() at
runtime, it walks the PCI tree up and down, and it isn't currently
protected against any changes or hotplug operation.

Hold the pci_bus_sem to protect it.

Link: https://lore.kernel.org/r/7339fd73ccaf58552737ab10008333fd9f7723f2.camel@kernel.crashing.org
Signed-off-by: Benjamin Herrenschmidt <[email protected]>
Signed-off-by: Bjorn Helgaas <[email protected]>

Author: ozbenh

drivers/pci/setup-bus.c

@@ -2066,6 +2066,8 @@ int pci_reassign_bridge_resources(struct pci_dev *bridge, unsigned long type)
 	unsigned int i;
 	int ret;
 
+	down_read(&pci_bus_sem);
+
 	/* Walk to the root hub, releasing bridge BARs when possible */
 	next = bridge;
 	do {
@@ -2100,8 +2102,10 @@ int pci_reassign_bridge_resources(struct pci_dev *bridge, unsigned long type)
 		next = bridge->bus ? bridge->bus->self : NULL;
 	} while (next);
 
-	if (list_empty(&saved))
+	if (list_empty(&saved)) {
+		up_read(&pci_bus_sem);
 		return -ENOENT;
+	}
 
 	__pci_bus_size_bridges(bridge->subordinate, &added);
 	__pci_bridge_assign_resources(bridge, &added, &failed);
@@ -2122,6 +2126,7 @@ int pci_reassign_bridge_resources(struct pci_dev *bridge, unsigned long type)
 	}
 
 	free_list(&saved);
+	up_read(&pci_bus_sem);
 	return 0;
 
 cleanup:
@@ -2150,6 +2155,7 @@ int pci_reassign_bridge_resources(struct pci_dev *bridge, unsigned long type)
 		pci_setup_bridge(bridge->subordinate);
 	}
 	free_list(&saved);
+	up_read(&pci_bus_sem);
 
 	return ret;
 }