[PATCH] PCI: Fix active state requirement in PME polling

[Alex Williamson <alex.williamson@redhat.com>]

The commit noted in fixes added a bogus requirement that runtime PM
managed devices need to be in the RPM_ACTIVE state for PME polling.
In fact, only devices in low power states should be polled.

However there's still a requirement that the device config space must
be accessible, which has implications for both the current state of
the polled device and the parent bridge, when present.  It's not
sufficient to assume the bridge remains in D0 and cases have been
observed where the bridge passes the D0 test, but the PM state
indicates RPM_SUSPENDING and config space of the polled device becomes
inaccessible during pci_pme_wakeup().

Therefore, since the bridge is already effectively required to be in
the RPM_ACTIVE state, formalize this in the code and elevate the PM
usage count to maintain the state while polling the subordinate
device.

Cc: Lukas Wunner <lukas@wunner.de>
Cc: Mika Westerberg <mika.westerberg@linux.intel.com>
Cc: Rafael J. Wysocki <rafael@kernel.org>
Fixes: d3fcd7360338 ("PCI: Fix runtime PM race with PME polling")
Reported-by: Sanath S <sanath.s@amd.com>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=218360
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
---
 drivers/pci/pci.c | 37 ++++++++++++++++++++++---------------
 1 file changed, 22 insertions(+), 15 deletions(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index bdbf8a94b4d0..764d7c977ef4 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -2433,29 +2433,36 @@ static void pci_pme_list_scan(struct work_struct *work)
 		if (pdev->pme_poll) {
 			struct pci_dev *bridge = pdev->bus->self;
 			struct device *dev = &pdev->dev;
-			int pm_status;
+			struct device *bdev = bridge ? &bridge->dev : NULL;
+			int bref = 0;
 
 			/*
-			 * If bridge is in low power state, the
-			 * configuration space of subordinate devices
-			 * may be not accessible
+			 * If we have a bridge, it should be in an active/D0
+			 * state or the configuration space of subordinate
+			 * devices may not be accessible or stable over the
+			 * course of the call.
 			 */
-			if (bridge && bridge->current_state != PCI_D0)
-				continue;
+			if (bdev) {
+				bref = pm_runtime_get_if_active(bdev, true);
+				if (!bref)
+					continue;
+
+				if (bridge->current_state != PCI_D0)
+					goto put_bridge;
+			}
 
 			/*
-			 * If the device is in a low power state it
-			 * should not be polled either.
+			 * The device itself should be suspended but config
+			 * space must be accessible, therefore it cannot be in
+			 * D3cold.
 			 */
-			pm_status = pm_runtime_get_if_active(dev, true);
-			if (!pm_status)
-				continue;
-
-			if (pdev->current_state != PCI_D3cold)
+			if (pm_runtime_suspended(dev) &&
+			    pdev->current_state != PCI_D3cold)
 				pci_pme_wakeup(pdev, NULL);
 
-			if (pm_status > 0)
-				pm_runtime_put(dev);
+put_bridge:
+			if (bref > 0)
+				pm_runtime_put(bdev);
 		} else {
 			list_del(&pme_dev->list);
 			kfree(pme_dev);
-- 
2.43.0