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    SubjectRe: [PATCH 5.4 260/320] PCI: pciehp: Fix infinite loop in IRQ handler upon power fault
    On Mon, Jan 24, 2022 at 07:44:04PM +0100, Greg Kroah-Hartman wrote:
    > From: Lukas Wunner <lukas@wunner.de>
    >
    > commit 23584c1ed3e15a6f4bfab8dc5a88d94ab929ee12 upstream.

    I would hold off on backporting the pciehp changes until we resolve
    this regression in v5.17-rc1:

    https://bugzilla.kernel.org/show_bug.cgi?id=215525

    > 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.
    >
    > Link: https://bugzilla.kernel.org/show_bug.cgi?id=214989
    > Link: https://lore.kernel.org/linux-pci/DM8PR11MB5702255A6A92F735D90A4446868B9@DM8PR11MB5702.namprd11.prod.outlook.com
    > Fixes: 8edf5332c393 ("PCI: pciehp: Fix MSI interrupt race")
    > Link: https://lore.kernel.org/r/66eaeef31d4997ceea357ad93259f290ededecfd.1637187226.git.lukas@wunner.de
    > Reported-by: Joseph Bao <joseph.bao@intel.com>
    > Tested-by: Joseph Bao <joseph.bao@intel.com>
    > Signed-off-by: Lukas Wunner <lukas@wunner.de>
    > Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
    > Cc: stable@vger.kernel.org # v4.19+
    > Cc: Stuart Hayes <stuart.w.hayes@gmail.com>
    > Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    > ---
    > drivers/pci/hotplug/pciehp_hpc.c | 7 ++++---
    > 1 file changed, 4 insertions(+), 3 deletions(-)
    >
    > --- a/drivers/pci/hotplug/pciehp_hpc.c
    > +++ b/drivers/pci/hotplug/pciehp_hpc.c
    > @@ -577,6 +577,8 @@ read_status:
    > */
    > 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) {
    > @@ -586,7 +588,7 @@ read_status:
    > }
    >
    > 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
    > @@ -660,8 +662,7 @@ static irqreturn_t pciehp_ist(int irq, v
    > }
    >
    > /* 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);
    >
    >

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