PCI: hv: Use async probing to reduce boot time

BugLink: https://bugs.launchpad.net/bugs/2023071
BugLink: https://bugs.launchpad.net/bugs/2023594

Commit 414428c ("PCI: hv: Lock PCI bus on device eject") added
pci_lock_rescan_remove() and pci_unlock_rescan_remove() in
create_root_hv_pci_bus() and in hv_eject_device_work() to address the
race between create_root_hv_pci_bus() and hv_eject_device_work(), but it
turns that grabing the pci_rescan_remove_lock mutex is not enough:
refer to the earlier fix "PCI: hv: Add a per-bus mutex state_lock".

Now with hbus->state_lock and other fixes, the race is resolved, so
remove pci_{lock,unlock}_rescan_remove() in create_root_hv_pci_bus():
this removes the serialization in hv_pci_probe() and hence allows
async-probing (PROBE_PREFER_ASYNCHRONOUS) to work.

Add the async-probing flag to hv_pci_drv.

pci_{lock,unlock}_rescan_remove() in hv_eject_device_work() and in
hv_pci_remove() are still kept: according to the comment before
drivers/pci/probe.c: static DEFINE_MUTEX(pci_rescan_remove_lock),
"PCI device removal routines should always be executed under this mutex".

Signed-off-by: Dexuan Cui <[email protected]>
Reviewed-by: Michael Kelley <[email protected]>
Reviewed-by: Long Li <[email protected]>
Cc: [email protected]
(backported from commit 08a9019ea35582f310946d193e5daab53931fd04 https://github.com/dcui/tdx.git)
[rtg - context adjustments]
Signed-off-by: Tim Gardner <[email protected]>
Acked-by: Philip Cox <[email protected]>
Acked-by: John Cabaj <[email protected]>
Signed-off-by: Tim Gardner <[email protected]>

Author: dcui

drivers/pci/controller/pci-hyperv.c

@@ -2288,12 +2288,16 @@ static int create_root_hv_pci_bus(struct hv_pcibus_device *hbus)
 	if (error)
 		return error;
 
-	pci_lock_rescan_remove();
 	hv_pci_assign_properties(hbus);
+	/*
+	 * pci_lock_rescan_remove() and pci_unlock_rescan_remove() are
+	 * unnecessary here, because we hold the hbus->state_lock, meaning
+	 * hv_eject_device_work() and pci_devices_present_work() can't race
+	 * with create_root_hv_pci_bus().
+	 */
 	pci_bus_assign_resources(bridge->bus);
 	hv_pci_assign_slots(hbus);
 	pci_bus_add_devices(bridge->bus);
-	pci_unlock_rescan_remove();
 	hbus->state = hv_pcibus_installed;
 	return 0;
 }
@@ -3969,6 +3973,9 @@ static struct hv_driver hv_pci_drv = {
 	.remove		= hv_pci_remove,
 	.suspend	= hv_pci_suspend,
 	.resume		= hv_pci_resume,
+	.driver = {
+		.probe_type = PROBE_PREFER_ASYNCHRONOUS,
+	},
 };
 
 static void __exit exit_hv_pci_drv(void)