[PATCH v2] PCI: mvebu: Dispose INTx IRQs before to removing INTx domain

["Marek Behún" <kabel@kernel.org>]

From: Pali Rohár <pali@kernel.org>

The documentation for the irq_domain_remove() function says that all
mappings within the IRQ domain must be disposed before the domain is
removed.

Currently, the INTx IRQs are not disposed in pci-mvebu driver .remove()
method, which causes the kernel to crash when unloading the driver and
then reading /sys/kernel/debug/irq/irqs/<num> or /proc/interrupts.

Unmapping of the IRQs at this point of the .remove() method is safe,
since the PCIe bus is already unregistered, and all its devices are
unbound from their drivers and removed. If there was indeed any
remaining use of PCIe resources, then it would mean that PCIe hotplug
code is broken, and we have bigger problems.

Fixes: ec075262648f ("PCI: mvebu: Implement support for legacy INTx interrupts")
Reported-by: Hajo Noerenberg <hajo-linux-bugzilla@noerenberg.de>
Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Marek Behún <kabel@kernel.org>
[ Marek: refactored a little, added more explanation to commit message ]
Signed-off-by: Marek Behún <kabel@kernel.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
---
Changes since v1:
- added explanation into commit message about why this is safe to do,
  as suggested by Andy. The explanation originally comes from Pali:
    https://lore.kernel.org/linux-arm-kernel/20220809133911.hqi7eyskcq2sojia@pali/
---
 drivers/pci/controller/pci-mvebu.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/controller/pci-mvebu.c b/drivers/pci/controller/pci-mvebu.c
index 29fe09c99e7d..91a02b23aeb1 100644
--- a/drivers/pci/controller/pci-mvebu.c
+++ b/drivers/pci/controller/pci-mvebu.c
@@ -1683,8 +1683,15 @@ static void mvebu_pcie_remove(struct platform_device *pdev)
 			irq_set_chained_handler_and_data(irq, NULL, NULL);
 
 		/* Remove IRQ domains. */
-		if (port->intx_irq_domain)
+		if (port->intx_irq_domain) {
+			for (int j = 0; j < PCI_NUM_INTX; j++) {
+				int virq = irq_find_mapping(port->intx_irq_domain, j);
+
+				if (virq > 0)
+					irq_dispose_mapping(virq);
+			}
 			irq_domain_remove(port->intx_irq_domain);
+		}
 
 		/* Free config space for emulated root bridge. */
 		pci_bridge_emul_cleanup(&port->bridge);
-- 
2.44.2