ACPI / hotplug / PCI: Execute _EJ0 under the ACPI scan lock

Since acpi_device_hotplug() assumes that ACPI handles of device
objects passed to it will not become invalid while acpi_scan_lock
is being held, make acpiphp_disable_slot() acquire acpi_scan_lock,
because it generally causes _EJ0 to be executed for one of the
devices in the slot and that may cause its ACPI handle to become
invalid.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/pci/hotplug/acpiphp_glue.c

@@ -1007,9 +1007,15 @@ int acpiphp_disable_slot(struct acpiphp_slot *slot)
 {
 	int ret;
 
+	/*
+	 * Acquire acpi_scan_lock to ensure that the execution of _EJ0 in
+	 * acpiphp_disable_and_eject_slot() will be synchronized properly.
+	 */
+	acpi_scan_lock_acquire();
 	pci_lock_rescan_remove();
 	ret = acpiphp_disable_and_eject_slot(slot);
 	pci_unlock_rescan_remove();
+	acpi_scan_lock_release();
 	return ret;
 }