On Thu, Mar 13, 2025 at 04:23:30PM +0200, Ilpo Järvinen wrote:
pciehp_reset_slot() disables PDCE (Presence Detect Changed Enable) and DLLSCE (Data Link Layer State Changed Enable) for the duration of reset and clears the related status bits PDC and DLLSC from the Slot Status register after the reset to avoid hotplug incorrectly assuming the card was removed.
However, hotplug shares interrupt with PME and BW notifications both of which can make pciehp_isr() to run despite PDCE and DLLSCE bits being off. pciehp_isr() then picks PDC or DLLSC bits from the Slot Status register due to the events that occur during reset and caches them into ->pending_events. Later, the IRQ thread in pciehp_ist() will process the ->pending_events and will assume the Link went Down due to a card change (in pciehp_handle_presence_or_link_change()).
Change pciehp_reset_slot() to also clear HPIE (Hot-Plug Interrupt Enable) as pciehp_isr() will first check HPIE to see if the interrupt is not for it. Then synchronize with the IRQ handling to ensure no events are pending, before invoking the reset.
After dwelling on this for a while, I'm thinking that it may re-introduce the issue fixed by commit f5eff5591b8f ("PCI: pciehp: Fix AB-BA deadlock between reset_lock and device_lock"):
Looking at the second and third stack trace in its commit message, down_write(reset_lock) in pciehp_reset_slot() is basically equivalent to synchronize_irq() and we're holding device_lock() at that point, hindering progress of pciehp_ist().
So I think I have guided you in the wrong direction and I apologize for that.
However it seems to me that this should be solvable with the small patch below. Am I missing something?
@Joel Mathew Thomas, could you give the below patch a spin and see if it helps?
Thanks!
-- >8 --
diff --git a/drivers/pci/hotplug/pciehp_hpc.c b/drivers/pci/hotplug/pciehp_hpc.c index bb5a8d9f03ad..99a2ac13a3d1 100644 --- a/drivers/pci/hotplug/pciehp_hpc.c +++ b/drivers/pci/hotplug/pciehp_hpc.c @@ -688,6 +688,11 @@ static irqreturn_t pciehp_isr(int irq, void *dev_id) return IRQ_HANDLED; }
+ /* Ignore events masked by pciehp_reset_slot(). */ + events &= ctrl->slot_ctrl; + if (!events) + return IRQ_HANDLED; + /* Save pending events for consumption by IRQ thread. */ atomic_or(events, &ctrl->pending_events); return IRQ_WAKE_THREAD;