linux-kernel - [PATCH v3 6/6] PCI: hv: Use async probing to reduce boot time

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Message-Id: <20230420024037.5921-7-decui@microsoft.com>
Date:   Wed, 19 Apr 2023 19:40:37 -0700
From:   Dexuan Cui <decui@...rosoft.com>
To:     bhelgaas@...gle.com, davem@...emloft.net, decui@...rosoft.com,
        edumazet@...gle.com, haiyangz@...rosoft.com, jakeo@...rosoft.com,
        kuba@...nel.org, kw@...ux.com, kys@...rosoft.com, leon@...nel.org,
        linux-pci@...r.kernel.org, lpieralisi@...nel.org,
        mikelley@...rosoft.com, pabeni@...hat.com, robh@...nel.org,
        saeedm@...dia.com, wei.liu@...nel.org, longli@...rosoft.com,
        boqun.feng@...il.com, ssengar@...rosoft.com, helgaas@...nel.org
Cc:     linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-rdma@...r.kernel.org, netdev@...r.kernel.org,
        josete@...rosoft.com, stable@...r.kernel.org
Subject: [PATCH v3 6/6] PCI: hv: Use async probing to reduce boot time

Commit 414428c5da1c ("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 <decui@...rosoft.com>
Reviewed-by: Michael Kelley <mikelley@...rosoft.com>
Reviewed-by: Long Li <longli@...rosoft.com>
Cc: stable@...r.kernel.org
---

v2:
  No change to the patch body.
  Improved the commit message [Michael Kelley]
  Added Cc:stable

v3:
  Added Michael's and Long Li's Reviewed-by.
  Fixed a typo in the commit message: grubing -> grabing [Thanks, Michael!]

 drivers/pci/controller/pci-hyperv.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
index 3ae2f99dea8c2..2ea2b1b8a4c9a 100644
--- a/drivers/pci/controller/pci-hyperv.c
+++ b/drivers/pci/controller/pci-hyperv.c
@@ -2312,12 +2312,16 @@ static int create_root_hv_pci_bus(struct hv_pcibus_device *hbus)
 	if (error)
 		return error;

-	pci_lock_rescan_remove();
+	/*
+	 * 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().
+	 */
 	hv_pci_assign_numa_node(hbus);
 	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;
 }
@@ -4003,6 +4007,9 @@ 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)
-- 
2.25.1