linux-kernel - [PATCH] PCI/PM: Prevent runtime suspend before devices are fully initialized

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Message-ID: <20251016155335.1.I60a53c170a8596661883bd2b4ef475155c7aa72b@changeid>
Date: Thu, 16 Oct 2025 15:53:35 -0700
From: Brian Norris <briannorris@...omium.org>
To: Bjorn Helgaas <bhelgaas@...gle.com>
Cc: linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org,
	"Rafael J . Wysocki" <rafael@...nel.org>,
	Lukas Wunner <lukas@...ner.de>,
	linux-pci@...r.kernel.org,
	Brian Norris <briannorris@...omium.org>,
	stable@...r.kernel.org
Subject: [PATCH] PCI/PM: Prevent runtime suspend before devices are fully initialized

PCI devices are created via pci_scan_slot() and similar, and are
promptly configured for runtime PM (pci_pm_init()). They are initially
prevented from suspending by way of pm_runtime_forbid(); however, it's
expected that user space may override this via sysfs [1].

Now, sometime after initial scan, a PCI device receives its BAR
configuration (pci_assign_unassigned_bus_resources(), etc.).

If a PCI device is allowed to suspend between pci_scan_slot() and
pci_assign_unassigned_bus_resources(), then pci-driver.c will
save/restore incorrect BAR configuration for the device, and the device
may cease to function.

This behavior races with user space, since user space may enable runtime
PM [1] as soon as it sees the device, which may be before BAR
configuration.

Prevent suspending in this intermediate state by holding a runtime PM
reference until the device is fully initialized and ready for probe().

[1] echo auto > /sys/bus/pci/devices/.../power/control

Cc: <stable@...r.kernel.org>
Signed-off-by: Brian Norris <briannorris@...omium.org>
---

 drivers/pci/bus.c | 7 +++++++
 drivers/pci/pci.c | 6 ++++++
 2 files changed, 13 insertions(+)

diff --git a/drivers/pci/bus.c b/drivers/pci/bus.c
index f26aec6ff588..227a8898acac 100644
--- a/drivers/pci/bus.c
+++ b/drivers/pci/bus.c
@@ -14,6 +14,7 @@
 #include <linux/of.h>
 #include <linux/of_platform.h>
 #include <linux/platform_device.h>
+#include <linux/pm_runtime.h>
 #include <linux/proc_fs.h>
 #include <linux/slab.h>

@@ -375,6 +376,12 @@ void pci_bus_add_device(struct pci_dev *dev)
 		put_device(&pdev->dev);
 	}

+	/*
+	 * Now that resources are assigned, drop the reference we grabbed in
+	 * pci_pm_init().
+	 */
+	pm_runtime_put_noidle(&dev->dev);
+
 	if (!dn || of_device_is_available(dn))
 		pci_dev_allow_binding(dev);

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index b14dd064006c..06a901214f2c 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -3226,6 +3226,12 @@ void pci_pm_init(struct pci_dev *dev)
 	pci_pm_power_up_and_verify_state(dev);
 	pm_runtime_forbid(&dev->dev);
 	pm_runtime_set_active(&dev->dev);
+	/*
+	 * We cannot allow a device to suspend before its resources are
+	 * configured. Otherwise, we may allow saving/restoring unexpected BAR
+	 * configuration.
+	 */
+	pm_runtime_get_noresume(&dev->dev);
 	pm_runtime_enable(&dev->dev);
 }

-- 
2.51.0.858.gf9c4a03a3a-goog