x86/PCI: Implement pcibios_release_device to release IRQ from IOAPIC

The revert of 991de2e590 ("PCI, x86: Implement pcibios_alloc_irq()
and pcibios_free_irq()") causes a problem for IOAPIC hotplug. The
problem is that IRQs are allocated and freed in pci_enable_device()
and pci_disable_device(). But there are some drivers which don't call
pci_disable_device(), and they have good reasons not calling it, so
if they're using IOAPIC their IRQs won't have a chance to be released
from the IOAPIC. When this happens IOAPIC hot-removal fails with a
kernel stack dump and an error message like this:

  [149335.697989] pin16 on IOAPIC2 is still in use.

It turns out that we can fix it in a different way without moving IRQ
allocation into pcibios_alloc_irq(), thus avoiding the regression of
991de2e590. We can keep the allocation and freeing of IRQs as is
within pci_enable_device()/pci_disable_device(), without breaking any
previous assumption of the rest of the system, keeping compatibility
with both the legacy and the modern drivers. We can accomplish this by
implementing the existing __weak hook of pcibios_release_device() thus
when a pci device is about to be deleted we get notified in the hook
and take the chance to release its IRQ, if any, from the IOAPIC.

Implement pcibios_release_device() for x86 to release any IRQ not released
by the driver.

Signed-off-by: Rui Wang <rui.y.wang@intel.com>
Cc: tony.luck@intel.com
Cc: linux-pci@vger.kernel.org
Cc: rjw@rjwysocki.net
Cc: linux-acpi@vger.kernel.org
Cc: fengguang.wu@intel.com
Cc: helgaas@kernel.org
Cc: kbuild-all@01.org
Cc: bhelgaas@google.com
Link: http://lkml.kernel.org/r/1488288869-31290-2-git-send-email-rui.y.wang@intel.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/pci/common.c

@@ -735,6 +735,15 @@ void pcibios_disable_device (struct pci_dev *dev)
 		pcibios_disable_irq(dev);
 }
 
+#ifdef CONFIG_ACPI_HOTPLUG_IOAPIC
+void pcibios_release_device(struct pci_dev *dev)
+{
+	if (atomic_dec_return(&dev->enable_cnt) >= 0)
+		pcibios_disable_device(dev);
+
+}
+#endif
+
 int pci_ext_cfg_avail(void)
 {
 	if (raw_pci_ext_ops)