Sorry for the delayed response. On Tue, Oct 22, 2024 at 09:02:43PM +0800, Chia-Lin Kao (AceLan) wrote: > 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. Can you explain what the race is, how it leads to a system hang, and how this change avoids it? I assume that .resume_noirq() for two devices in the same PCIe path, e.g., a dock and a device downstream from it, would be serialized at a higher level, because we would want to resume the upstream device before trying to resume the downstream one. But you're seeing something different? > 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. The code change is in the pciehp_device_replaced() path. When you reproduce the problem, do you actually replace a device? Or is something wrong with the pciehp_device_replaced() checks, and we mistakenly *think* a device was replaced? > Changes: > v2: > * Replace pciehp_request() with atomic_or() to fix race condition > > v1: > * https://lore.kernel.org/lkml/Zvf7xYEA32VgLRJ6@xxxxxxxxx/T/ > * Remove pci_walk_bus() call > * Fix appeared to work due to lower reproduction rate Thanks for including the changelog. You can put it after "---", because we don't include it in the commit anyway. You can wrap the commit log to 75 columns so it fits in 80 even after git log indents it. > Fixes: 9d573d19547b ("PCI: pciehp: Detect device replacement during system sleep") > Signed-off-by: Chia-Lin Kao (AceLan) <acelan.kao@xxxxxxxxxxxxx> > --- > 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 >
