linux-kernel - [PATCH v5] PCI/PM: Prevent runtime suspend until devices are fully initialized

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Message-ID: <20260122094815.v5.1.I60a53c170a8596661883bd2b4ef475155c7aa72b@changeid>
Date: Thu, 22 Jan 2026 09:48:15 -0800
From: Brian Norris <briannorris@...omium.org>
To: Bjorn Helgaas <bhelgaas@...gle.com>
Cc: linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org,
	Lukas Wunner <lukas@...ner.de>,
	linux-pm@...r.kernel.org,
	"Rafael J . Wysocki" <rafael@...nel.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
	Brian Norris <briannorris@...omium.org>
Subject: [PATCH v5] PCI/PM: Prevent runtime suspend until devices are fully initialized

Previously, it was possible for a PCI device to be runtime-suspended before
it was fully initialized. When that happened, the suspend process could
save invalid device state, for example, before BAR assignment. Restoring
the invalid state during resume may leave the device non-functional.

Prevent runtime suspend for PCI devices until they are fully initialized by
deferring pm_runtime_enable().

More details on how exactly this may occur:

  1. PCI device is created by pci_scan_slot() or similar

  2. As part of pci_scan_slot(), pci_pm_init() puts the device in D0 and
     prevents runtime suspend prevented via pm_runtime_forbid()

  3. pci_device_add() adds the underlying 'struct device' via device_add(),
     which means user space can allow runtime suspend, e.g.,

       echo auto > /sys/bus/pci/devices/.../power/control

  4. PCI device receives BAR configuration
     (pci_assign_unassigned_bus_resources(), etc.)

  5. pci_bus_add_device() applies final fixups, saves device state, and
     tries to attach a driver

The device may potentially be suspended between #3 and #5, so this is racy
with user space (udev or similar).

Many PCI devices are enumerated at subsys_initcall time and so will not
race with user space, but devices created later by hotplug or modular
pwrctrl or host controller drivers are susceptible to this race.

More runtime PM details at the first Link: below.

Signed-off-by: Brian Norris <briannorris@...omium.org>
Tested-by: Marek Szyprowski <m.szyprowski@...sung.com>
Cc: stable@...r.kernel.org
Link: https://lore.kernel.org/all/20251016155335.1.I60a53c170a8596661883bd2b4ef475155c7aa72b@changeid/
Link: https://lore.kernel.org/all/0e35a4e1-894a-47c1-9528-fc5ffbafd9e2@samsung.com/

Link: https://lore.kernel.org/all/20251016155335.1.I60a53c170a8596661883bd2b4ef475155c7aa72b@changeid/
Cc: <stable@...r.kernel.org>
---

Changes in v5:
 * Put pm_runtime_set_active() back where it was, to ensure our parent
   can't suspend before we're really ready. (See bug report in 2nd
   "Link:")
 * Add comments
 * Update commit description with Bjorn's rewrite
 * Add Marek's Tested-by

Changes in v4:
 * Move pm_runtime_set_active() too

Changes in v3:
 * Add Link to initial discussion
 * Add Rafael's Reviewed-by
 * Add lengthier footnotes about forbid vs allow vs sysfs

Changes in v2:
 * Update CC list
 * Rework problem description
 * Update solution: defer pm_runtime_enable(), instead of trying to
   get()/put()

 drivers/pci/bus.c | 7 +++++++
 drivers/pci/pci.c | 5 ++++-
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/bus.c b/drivers/pci/bus.c
index 4383a36fd6ca..90954f81962b 100644
--- a/drivers/pci/bus.c
+++ b/drivers/pci/bus.c
@@ -15,6 +15,7 @@
 #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>
 
@@ -379,6 +380,12 @@ void pci_bus_add_device(struct pci_dev *dev)
 		put_device(&pdev->dev);
 	}
 
+	/*
+	 * Enable runtime PM (and potentially suspend) only after we've fully
+	 * configured the PCI state.
+	 */
+	pm_runtime_enable(&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 13dbb405dc31..07b0d029aa51 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -3196,8 +3196,11 @@ void pci_pm_init(struct pci_dev *dev)
 poweron:
 	pci_pm_power_up_and_verify_state(dev);
 	pm_runtime_forbid(&dev->dev);
+	/*
+	 * Mark ourselves active now, to prevent our parent from suspending
+	 * while we finish configuring the PCI device.
+	 */
 	pm_runtime_set_active(&dev->dev);
-	pm_runtime_enable(&dev->dev);
 }
 
 static unsigned long pci_ea_flags(struct pci_dev *dev, u8 prop)
-- 
2.52.0.457.g6b5491de43-goog