restore_dev_resource() copies saved addresses and flags from the struct
pci_dev_resource back to the struct resource, typically, during
rollback from a failure or in preparation for a retry attempt.

If the resource is within resource tree, the resource must not be
modified as the resource tree could be corrupted. Thus, it's a bug to
call restore_dev_resource() for assigned resources (which did happen
due to logic flaws in the BAR resize rollback).

Add WARN_ON_ONCE() into restore_dev_resource() to detect such bugs
easily and return without altering the resource to prevent corruption.

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
---
 drivers/pci/setup-bus.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
index 8da83b612c59..28d6ae822c0b 100644
--- a/drivers/pci/setup-bus.c
+++ b/drivers/pci/setup-bus.c
@@ -15,6 +15,7 @@
  */
 
 #include <linux/bitops.h>
+#include <linux/bug.h>
 #include <linux/init.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
@@ -135,6 +136,9 @@ static void restore_dev_resource(struct pci_dev_resource *dev_res)
 {
 	struct resource *res = dev_res->res;
 
+	if (WARN_ON_ONCE(res->parent))
+		return;
+
 	res->start = dev_res->start;
 	res->end = dev_res->end;
 	res->flags = dev_res->flags;
-- 
2.39.5