PCI: WARN (not BUG()) when we fail to assign optional resources

JIRA: https://issues.redhat.com/browse/RHEL-107597
Upstream Status: af6e3de

commit af6e3de
Author: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Date:   Mon May 12 00:52:23 2025 +0300

    PCI: WARN (not BUG()) when we fail to assign optional resources

    Resource fitting/assignment code checks if there's a remainder in
    add_list (aka. realloc_head in the inner functions) using BUG_ON().
    This problem typically results in a mere PCI device resource assignment
    failure which does not warrant using BUG_ON(). The machine could well
    come up usable even if this condition occurs because the realloc_head
    relates to resources which are optional anyway.

    Change BUG_ON() to WARN_ON_ONCE() and free the list if it's not empty.

    [bhelgaas: subject]
    Reported-by: Tudor Ambarus <tudor.ambarus@linaro.org>
    Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
    Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
    Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
    Link: https://lore.kernel.org/linux-pci/5f103643-5e1c-43c6-b8fe-9617d3b5447c@linaro.org
    Link: https://lore.kernel.org/r/20250511215223.7131-1-ilpo.jarvinen@linux.intel.com

Signed-off-by: Myron Stowe <mstowe@redhat.com>

Author: Myron Stowe

drivers/pci/setup-bus.c

@@ -2302,8 +2302,8 @@ void pci_assign_unassigned_root_bus_resources(struct pci_bus *bus)
 
 		/* Depth last, allocate resources and update the hardware. */
 		__pci_bus_assign_resources(bus, add_list, &fail_head);
-		if (add_list)
-			BUG_ON(!list_empty(add_list));
+		if (WARN_ON_ONCE(add_list && !list_empty(add_list)))
+			free_list(add_list);
 		tried_times++;
 
 		/* Any device complain? */
@@ -2365,7 +2365,8 @@ void pci_assign_unassigned_bridge_resources(struct pci_dev *bridge)
 		pci_bridge_distribute_available_resources(bridge, &add_list);
 
 		__pci_bridge_assign_resources(bridge, &add_list, &fail_head);
-		BUG_ON(!list_empty(&add_list));
+		if (WARN_ON_ONCE(!list_empty(&add_list)))
+			free_list(&add_list);
 		tried_times++;
 
 		if (list_empty(&fail_head))
@@ -2441,7 +2442,8 @@ int pci_reassign_bridge_resources(struct pci_dev *bridge, unsigned long type)
 
 	__pci_bus_size_bridges(bridge->subordinate, &added);
 	__pci_bridge_assign_resources(bridge, &added, &failed);
-	BUG_ON(!list_empty(&added));
+	if (WARN_ON_ONCE(!list_empty(&added)))
+		free_list(&added);
 
 	if (!list_empty(&failed)) {
 		ret = -ENOSPC;
@@ -2497,6 +2499,7 @@ void pci_assign_unassigned_bus_resources(struct pci_bus *bus)
 			__pci_bus_size_bridges(dev->subordinate, &add_list);
 	up_read(&pci_bus_sem);
 	__pci_bus_assign_resources(bus, &add_list, NULL);
-	BUG_ON(!list_empty(&add_list));
+	if (WARN_ON_ONCE(!list_empty(&add_list)))
+		free_list(&add_list);
 }
 EXPORT_SYMBOL_GPL(pci_assign_unassigned_bus_resources);