A system hang occurs when multiple PCIe hotplug controllers in a daisy-chained
setup (like a Thunderbolt dock with NVMe storage) resume from system sleep.
This happens when both the dock and its downstream devices try to process PDC
events at the same time through pciehp_request().

This patch changes pciehp_request() to atomic_or(), which adds the PDC event to
ctrl->pending_events atomically. This change prevents the race condition by
making the event handling atomic across multiple hotplug controllers during
resume.

The bug was found with an Intel Thunderbolt 4 Bridge (8086:0b26) dock and a
Phison NVMe controller (1987:5012), where the system would hang if both devices
tried to handle presence detect changes during resume.

Changes:
  v2:
    * Replace pciehp_request() with atomic_or() to fix race condition

  v1:
    * https://lore.kernel.org/lkml/Zvf7xYEA32VgLRJ6@wunner.de/T/
    * Remove pci_walk_bus() call
    * Fix appeared to work due to lower reproduction rate

Fixes: 9d573d19547b ("PCI: pciehp: Detect device replacement during system sleep")
Signed-off-by: Chia-Lin Kao (AceLan) <acelan.kao@canonical.com>
---
 drivers/pci/hotplug/pciehp_core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/pci/hotplug/pciehp_core.c b/drivers/pci/hotplug/pciehp_core.c
index ff458e692fed..56bf23d55c41 100644
--- a/drivers/pci/hotplug/pciehp_core.c
+++ b/drivers/pci/hotplug/pciehp_core.c
@@ -332,7 +332,7 @@ static int pciehp_resume_noirq(struct pcie_device *dev)
 			ctrl_dbg(ctrl, "device replaced during system sleep\n");
 			pci_walk_bus(ctrl->pcie->port->subordinate,
 				     pci_dev_set_disconnected, NULL);
-			pciehp_request(ctrl, PCI_EXP_SLTSTA_PDC);
+			atomic_or(PCI_EXP_SLTSTA_PDC, &ctrl->pending_events);
 		}
 	}
 
-- 
2.43.0