linux-kernel - Re: 584c5c422f6c ("x86/ioapic: Support hot-removal of IOAPICs present during boot")

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Date:   Sat, 10 Sep 2016 23:03:29 +0800
From:   Rui Wang <rui.y.wang@...el.com>
To:     bp@...en8.de
Cc:     bhelgaas@...gle.com, torvalds@...ux-foundation.org,
        peterz@...radead.org, tglx@...utronix.de, helgaas@...nel.org,
        linux-acpi@...r.kernel.org, linux-pci@...r.kernel.org,
        rjw@...ysocki.net, tony.luck@...el.com, mingo@...nel.org,
        x86@...nel.org, linux-kernel@...r.kernel.org, rui.y.wang@...el.com
Subject: Re: 584c5c422f6c ("x86/ioapic: Support hot-removal of IOAPICs present during boot")

On Sat, Sep 10, 2016 10:31 PM, Borislav Petkov wrote:
> 
> On Sat, Sep 10, 2016 at 09:11:30PM +0800, Rui Wang wrote:
> > Thanks for the analysis. Looks like acpi_gbl_root_node == 0. It is
> 
> Is ACPI_HANDLE(root_bus->bridge) == ACPI_ROOT_OBJECT?
> 
> Because this is what the code does but I can't see it from the code that the
> handle is of type ACPI_ROOT_OBJECT...
> 

I seem to have the clue. It is because ACPI_HANDLE(root_bus->bridge) == NULL.
Then this root bridge doesn't have a corresponding ACPI device. In this case
we shouldn't call acpi_ioapic_add(). This can be true for some old platforms.

If that's the case then the patch below can fix it.

Thanks
Rui

>From b37d806c78e5eea70dbb890c1e3dbb8b7e5038e6 Mon Sep 17 00:00:00 2001
From: Rui Wang <rui.y.wang@...el.com>
Date: Sat, 10 Sep 2016 10:56:34 -0400
Subject: [PATCH] x86/ioapic: Ignore root bridges without a companion ACPI device

Some PCI root bridges don't have a corresponding ACPI device.
Don't call acpi_ioapic_add() on these bridges because they can't
support ioapic hotplug.

Signed-off-by: Rui Wang <rui.y.wang@...el.com>
---
 drivers/pci/setup-bus.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
index ec538d3..2b05ac6 100644
--- a/drivers/pci/setup-bus.c
+++ b/drivers/pci/setup-bus.c
@@ -1852,10 +1852,15 @@ dump:
 void __init pci_assign_unassigned_resources(void)
 {
 	struct pci_bus *root_bus;
+	acpi_handle root_handle;
 
 	list_for_each_entry(root_bus, &pci_root_buses, node) {
 		pci_assign_unassigned_root_bus_resources(root_bus);
-		acpi_ioapic_add(ACPI_HANDLE(root_bus->bridge));
+		root_handle = ACPI_HANDLE(root_bus->bridge);
+
+		/* make sure the root bridge has a companion ACPI device */
+		if (root_handle)
+			acpi_ioapic_add(root_handle);
 	}
 }
 
-- 
1.8.3.1