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Subject[PATCH 5.4 260/320] PCI: pciehp: Fix infinite loop in IRQ handler upon power fault
From: Lukas Wunner <>

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.

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")
Reported-by: Joseph Bao <>
Tested-by: Joseph Bao <>
Signed-off-by: Lukas Wunner <>
Signed-off-by: Bjorn Helgaas <>
Cc: # v4.19+
Cc: Stuart Hayes <>
Signed-off-by: Greg Kroah-Hartman <>
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,

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