On Wed, Nov 17, 2021 at 11:22:09PM +0100, Lukas Wunner wrote:
> The Power Fault Detected bit in the Slot Status register differs from
> all other hotplug events in that it is sticky: It can only be cleared
> after turning off slot power. Per PCIe r5.0, sec. 6.7.1.8:
>
> If a power controller detects a main power fault on the hot-plug slot,
> it must automatically set its internal main power fault latch [...].
> The main power fault latch is cleared when software turns off power to
> the hot-plug slot.
>
> The stickiness used to cause interrupt storms and infinite loops which
> were fixed in 2009 by commits 5651c48cfafe ("PCI pciehp: fix power fault
> interrupt storm problem") and 99f0169c17f3 ("PCI: pciehp: enable
> software notification on empty slots").
>
> Unfortunately in 2020 the infinite loop issue was inadvertently
> reintroduced by commit 8edf5332c393 ("PCI: pciehp: Fix MSI interrupt
> race"): The hardirq handler pciehp_isr() clears the PFD bit until
> pciehp's power_fault_detected flag is set. That happens in the IRQ
> thread pciehp_ist(), which never learns of the event because the hardirq
> handler is stuck in an infinite loop. Fix by setting the
> power_fault_detected flag already in the hardirq handler.
>
> Fixes: 8edf5332c393 ("PCI: pciehp: Fix MSI interrupt race")
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=214989
> Link: https://lore.kernel.org/linux-pci/DM8PR11MB5702255A6A92F735D90A4446868B9@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> Reported-by: Joseph Bao <joseph.bao@xxxxxxxxx>
> Tested-by: Joseph Bao <joseph.bao@xxxxxxxxx>
> Signed-off-by: Lukas Wunner <lukas@xxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx # v4.19+
> Cc: Stuart Hayes <stuart.w.hayes@xxxxxxxxx>
Applied to pci/hotplug for v5.17, thanks very much!
> ---
> drivers/pci/hotplug/pciehp_hpc.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/pci/hotplug/pciehp_hpc.c b/drivers/pci/hotplug/pciehp_hpc.c
> index 83a0fa119cae..9535c61cbff3 100644
> --- a/drivers/pci/hotplug/pciehp_hpc.c
> +++ b/drivers/pci/hotplug/pciehp_hpc.c
> @@ -642,6 +642,8 @@ static irqreturn_t pciehp_isr(int irq, void *dev_id)
> */
> if (ctrl->power_fault_detected)
> status &= ~PCI_EXP_SLTSTA_PFD;
> + else if (status & PCI_EXP_SLTSTA_PFD)
> + ctrl->power_fault_detected = true;
>
> events |= status;
> if (!events) {
> @@ -651,7 +653,7 @@ static irqreturn_t pciehp_isr(int irq, void *dev_id)
> }
>
> if (status) {
> - pcie_capability_write_word(pdev, PCI_EXP_SLTSTA, events);
> + pcie_capability_write_word(pdev, PCI_EXP_SLTSTA, status);
>
> /*
> * In MSI mode, all event bits must be zero before the port
> @@ -725,8 +727,7 @@ static irqreturn_t pciehp_ist(int irq, void *dev_id)
> }
>
> /* Check Power Fault Detected */
> - if ((events & PCI_EXP_SLTSTA_PFD) && !ctrl->power_fault_detected) {
> - ctrl->power_fault_detected = 1;
> + if (events & PCI_EXP_SLTSTA_PFD) {
> ctrl_err(ctrl, "Slot(%s): Power fault\n", slot_name(ctrl));
> pciehp_set_indicators(ctrl, PCI_EXP_SLTCTL_PWR_IND_OFF,
> PCI_EXP_SLTCTL_ATTN_IND_ON);
> --
> 2.33.0
>
