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    Subject[PATCH 5.15 702/846] PCI: pciehp: Fix infinite loop in IRQ handler upon power fault
    Date
    From: Lukas Wunner <lukas@wunner.de>

    commit 23584c1ed3e15a6f4bfab8dc5a88d94ab929ee12 upstream.

    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
    @@ -642,6 +642,8 @@ 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) {
    @@ -651,7 +653,7 @@ 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
    @@ -725,8 +727,7 @@ 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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