linux-kernel - [PATCH 1/1] pci: Add subordinate check before pci_add_new

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Message-ID: <20250814093937.2372441-1-rui.he@windriver.com>
Date: Thu, 14 Aug 2025 17:39:37 +0800
From: Rui He <rui.he@...driver.com>
To: Bjorn Helgaas <bhelgaas@...gle.com>
CC: <linux-pci@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <Prashant.Chikhalkar@...driver.com>, <Jiguang.Xiao@...driver.com>,
        <Rui.He@...driver.com>
Subject: [PATCH 1/1] pci: Add subordinate check before pci_add_new_bus()

For preconfigured PCI bridge, child bus created on the first scan.
While for some reasons(e.g register mutation), the secondary, and subordiante
register reset to 0 on the second scan, which caused to create
PCI bus twice for the same PCI device.

Following is the related log:
[Wed May 28 20:38:36 CST 2025] pci 0000:0b:01.0: PCI bridge to [bus 0d]
[Wed May 28 20:38:36 CST 2025] pci 0000:0b:05.0: bridge configuration invalid ([bus 00-00]), reconfiguring
[Wed May 28 20:38:36 CST 2025] pci 0000:0b:01.0: PCI bridge to [bus 0e-10]
[Wed May 28 20:38:36 CST 2025] pci 0000:0b:05.0: PCI bridge to [bus 0f-10]

Here PCI device 000:0b:01.0 assigend to bus 0d and 0e.

This patch checks if child PCI bus has been created on the second scan
of bridge. If yes, return directly instead of create a new one.

Signed-off-by: Rui He <rui.he@...driver.com>
---
 drivers/pci/probe.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index f41128f91ca76..ec67adbf31738 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -1444,6 +1444,9 @@ static int pci_scan_bridge_extend(struct pci_bus *bus, struct pci_dev *dev,
 			goto out;
 		}
 
+		if(pci_has_subordinate(dev))
+			goto out;
+
 		/* Clear errors */
 		pci_write_config_word(dev, PCI_STATUS, 0xffff);
 
-- 
2.43.0