Subject: [PATCH 5/6] PCI: hv: Add a per-bus mutex state_lock

From: Dexuan Cui <[email-masked]>
Date: Mon, 27 Mar 2023 21:51:21 -0700

In the case of fast device addition/removal, it's possible that
hv_eject_device_work() can start to run before create_root_hv_pci_bus()
starts to run; as a result, the pci_get_domain_bus_and_slot() in
hv_eject_device_work() can return a 'pdev' of NULL, and
hv_eject_device_work() can remove the 'hpdev', and immediately send a
message PCI_EJECTION_COMPLETE to the host, and the host immediately
unassigns the PCI device from the guest; meanwhile,
create_root_hv_pci_bus() and the PCI device driver can be probing the
dead PCI device and reporting timeout errors.

Fix the issue by adding a per-bus mutex 'state_lock' and grabbing the
mutex before powering on the PCI bus in hv_pci_enter_d0(): when
hv_eject_device_work() starts to run, it's able to find the 'pdev' and call
pci_stop_and_remove_bus_device(pdev): if the PCI device driver has
loaded, the PCI device driver's probe() function is already called in
create_root_hv_pci_bus() -> pci_bus_add_devices(), and now
hv_eject_device_work() -> pci_stop_and_remove_bus_device() is able
to call the PCI device driver's remove() function and remove the device
reliably; if the PCI device driver hasn't loaded yet, the function call
hv_eject_device_work() -> pci_stop_and_remove_bus_device() is able to
remove the PCI device reliably and the PCI device driver's probe()
function won't be called; if the PCI device driver's probe() is already
running (e.g., systemd-udev is loading the PCI device driver), it must
be holding the per-device lock, and after the probe() finishes and releases
the lock, hv_eject_device_work() -> pci_stop_and_remove_bus_device() is
able to proceed to remove the device reliably.

Fixes: 4daace0d8ce8 ("PCI: hv: Add paravirtual PCI front-end for Microsoft Hyper-V VMs")
Signed-off-by: Dexuan Cui <[email-masked]>

---
 drivers/pci/controller/pci-hyperv.c | 27 +++++++++++++++++++++++++--
 1 file changed, 25 insertions(+), 2 deletions(-)

With the below debug code:

Changes to /drivers/net/ethernet/mellanox/mlx5/core/main.c
@@ -1727,6 +1727,8 @@ static int probe_one(struct pci_dev *pdev, const struct pci_device_id *id)
 	struct devlink *devlink;
 	int err;

+	printk("%s: line %d: sleep 20s: \n", __func__, __LINE__); ssleep(20);
+	printk("%s: line %d: sleep 20s: done\n", __func__, __LINE__);
 	devlink = mlx5_devlink_alloc(&pdev->dev);
 	if (!devlink) {
 		dev_err(&pdev->dev, "devlink alloc failed\n");
Changes to drivers/pci/controller/pci-hyperv.c
@@ -2749,6 +2749,7 @@ static void hv_eject_device_work(struct work_struct *work)
 	 */
 	wslot = wslot_to_devfn(hpdev->desc.win_slot.slot);
 	pdev = pci_get_domain_bus_and_slot(hbus->bridge->domain_nr, 0, wslot);
+	printk("%s: 1: line %d: pdev=%px\n", __func__, __LINE__, pdev);
 	if (pdev) {
 		pci_lock_rescan_remove();
 		pci_stop_and_remove_bus_device(pdev);
@@ -2756,9 +2757,12 @@ static void hv_eject_device_work(struct work_struct *work)
 		pci_unlock_rescan_remove();
 	}

+	printk("%s: 2: line %d: pdev=%px: sleeping 10s\n", __func__, __LINE__, pdev); ssleep(10);
+	printk("%s: 3: line %d: pdev=%px: sleeping 10s: done: removing hpdev\n", __func__, __LINE__, pdev);
 	spin_lock_irqsave(&hbus->device_list_lock, flags);
 	list_del(&hpdev->list_entry);
 	spin_unlock_irqrestore(&hbus->device_list_lock, flags);
+	printk("%s: 4: line %d: pdev=%px: hpdev is removed!!!\n", __func__, __LINE__, pdev);

 	if (hpdev->pci_slot)
 		pci_destroy_slot(hpdev->pci_slot);
@@ -2770,6 +2774,7 @@ static void hv_eject_device_work(struct work_struct *work)
 	vmbus_sendpacket(hbus->hdev->channel, ejct_pkt,
 			 sizeof(*ejct_pkt), 0,
 			 VM_PKT_DATA_INBAND, 0);
+	printk("%s: 5: line %d: pdev=%px: sent PCI_EJECTION_COMPLETE\n", __func__, __LINE__, pdev);

 	/* For the get_pcichild() in hv_pci_eject_device() */
 	put_pcichild(hpdev);
@@ -3686,7 +3691,10 @@ static int hv_pci_probe(struct hv_device *hdev,

 	hbus->state = hv_pcibus_probed;

+	printk("%s: line %d: create_root_hv_pci_bus=%d: sleeping 10s\n", __func__, __LINE__, ret); ssleep(10);
+	printk("%s: line %d: create_root_hv_pci_bus=%d: sleeping 10s: done\n", __func__, __LINE__, ret);
 	ret = create_root_hv_pci_bus(hbus);
+	printk("%s: line %d: create_root_hv_pci_bus=%d\n", __func__, __LINE__, ret);
 	if (ret)
 		goto free_windows;

I'm able to repro the below timeout errors (remove the PCI VF NIC within 10 seconds after it's assigned)

[   31.445306] hv_pci b92a0085-468b-407a-a88a-d33fac8edc75: PCI VMBus probing: Using version 0x10004
[   31.452133] hv_pci_probe: line 3694: create_root_hv_pci_bus=0: sleeping 10s
[   34.345256] hv_eject_device_work: 1: line 2752: pdev=0000000000000000
[   34.350175] hv_eject_device_work: 2: line 2760: pdev=0000000000000000: sleeping 10s
[   41.650330] hv_pci_probe: line 3695: create_root_hv_pci_bus=0: sleeping 10s: done
[   41.668443] hv_pci b92a0085-468b-407a-a88a-d33fac8edc75: PCI host bridge to bus 468b:00
[   41.674201] pci_bus 468b:00: root bus resource [mem 0xfe0000000-0xfe00fffff window]
[   41.680284] pci_bus 468b:00: No busn resource found for root bus, will use [bus 00-ff]
[   41.688901] pci 468b:00:02.0: [15b3:1016] type 00 class 0x020000
[   41.695554] pci 468b:00:02.0: reg 0x10: [mem 0xfe0000000-0xfe00fffff 64bit pref]
[   41.704304] pci 468b:00:02.0: enabling Extended Tags
...
[   41.745847] hv_pci_probe: line 3697: create_root_hv_pci_bus=0
[   41.938950] mlx5_core 468b:00:02.0: no default pinctrl state
[   41.941462] probe_one: line 1730: sleep 20s:
[   44.466334] hv_eject_device_work: 3: line 2761: pdev=0000000000000000: sleeping 10s: done: removing hpdev
[   44.472691] hv_eject_device_work: 4: line 2765: pdev=0000000000000000: hpdev is removed!!!
[   44.478007] hv_eject_device_work: 5: line 2777: pdev=0000000000000000: sent PCI_EJECTION_COMPLETE
[   44.480213] hv_netvsc 818fe754-b912-4445-af51-1f584812e3c9 eth0: VF slot 1 removed
[   63.154376] probe_one: line 1731: sleep 20s: done
[   63.161610] mlx5_core 468b:00:02.0: firmware version: 65535.65535.65535
[   83.174538] mlx5_core 468b:00:02.0: wait_fw_init:199:(pid 17): Waiting for FW initialization, timeout abort in 100s (0xffffffff)
[  103.190543] mlx5_core 468b:00:02.0: wait_fw_init:199:(pid 17): Waiting for FW initialization, timeout abort in 79s (0xffffffff)
[  123.202507] mlx5_core 468b:00:02.0: wait_fw_init:199:(pid 17): Waiting for FW initialization, timeout abort in 59s (0xffffffff)
[  143.214547] mlx5_core 468b:00:02.0: wait_fw_init:199:(pid 17): Waiting for FW initialization, timeout abort in 39s (0xffffffff)
[  163.222594] mlx5_core 468b:00:02.0: wait_fw_init:199:(pid 17): Waiting for FW initialization, timeout abort in 19s (0xffffffff)
[  183.178629] mlx5_core 468b:00:02.0: mlx5_function_setup:1130:(pid 17): Firmware over 120000 MS in pre-initializing state, aborting
[  183.186289] mlx5_core 468b:00:02.0: probe_one:1764:(pid 17): mlx5_init_one failed with error code -16
[  183.192623] mlx5_core: probe of 468b:00:02.0 failed with error -16
[  183.202701] pci_bus 468b:00: busn_res: [bus 00] is released

With the fix, I'm no longer seeing the timeout errors:

[   31.144066] hv_pci b92a0085-468b-407a-a88a-d33fac8edc75: PCI VMBus probing: Using version 0x10004
[   31.149207] hv_pci_probe: line 3708: create_root_hv_pci_bus=0: sleeping 10s
[   41.378274] hv_pci_probe: line 3709: create_root_hv_pci_bus=0: sleeping 10s: done
[   41.397577] hv_pci b92a0085-468b-407a-a88a-d33fac8edc75: PCI host bridge to bus 468b:00
[   41.402799] pci_bus 468b:00: root bus resource [mem 0xfe0000000-0xfe00fffff window]
...
[   41.415586] pci 468b:00:02.0: [15b3:1016] type 00 class 0x020000
[   41.423132] pci 468b:00:02.0: reg 0x10: [mem 0xfe0000000-0xfe00fffff 64bit pref]
...
[   41.471366] hv_pci_probe: line 3711: create_root_hv_pci_bus=0
[   41.484371] hv_eject_device_work: 1: line 2761: pdev=ffff90f4c4858000
[   41.491644] hv_eject_device_work: 2: line 2769: pdev=ffff90f4c4858000: sleeping 10s
[   51.618268] hv_eject_device_work: 3: line 2770: pdev=ffff90f4c4858000: sleeping 10s: done: removing hpdev
[   51.625094] hv_eject_device_work: 4: line 2774: pdev=ffff90f4c4858000: hpdev is removed!!!
[   51.630234] hv_eject_device_work: 5: line 2786: pdev=ffff90f4c4858000: sent PCI_EJECTION_COMPLETE
[   51.632148] hv_netvsc 818fe754-b912-4445-af51-1f584812e3c9 eth0: VF slot 1 removed
[   51.647014] pci_bus 468b:00: busn_res: [bus 00] is released

Now the mlx5_core driver is loaded; I try fast device addition/removal again
and I'm still not seeing the timeout errors:

[  495.622678] hv_pci b92a0085-468b-407a-a88a-d33fac8edc75: PCI VMBus probing: Using version 0x10004
[  495.627791] hv_pci_probe: line 3708: create_root_hv_pci_bus=0: sleeping 10s
[  505.762550] hv_pci_probe: line 3709: create_root_hv_pci_bus=0: sleeping 10s: done
[  505.779496] hv_pci b92a0085-468b-407a-a88a-d33fac8edc75: PCI host bridge to bus 468b:00
[  505.784872] pci_bus 468b:00: root bus resource [mem 0xfe0000000-0xfe00fffff window]
...
[  505.798323] pci 468b:00:02.0: [15b3:1016] type 00 class 0x020000
...
[  505.868908] probe_one: line 1730: sleep 20s:
[  525.986578] probe_one: line 1731: sleep 20s: done
[  525.990717] mlx5_core 468b:00:02.0: enabling device (0000 -> 0002)
[  525.998339] mlx5_core 468b:00:02.0: firmware version: 14.25.8102
...
[  526.381211] hv_netvsc 818fe754-b912-4445-af51-1f584812e3c9 eth0: VF registering: eth1
[  526.385432] mlx5_core 468b:00:02.0 eth1: joined to eth0
[  526.389076] mlx5_core 468b:00:02.0 eth1: Disabling LRO, not supported in legacy RQ
[  526.397276] mlx5_core 468b:00:02.0 eth1: Disabling LRO, not supported in legacy RQ
[  526.400330] mlx5_core 468b:00:02.0: MLX5E: StrdRq(0) RqSz(1024) StrdSz(256) RxCqeCmprss(0 basic)
...
[  526.430803] hv_pci_probe: line 3711: create_root_hv_pci_bus=0
[  526.443633] hv_eject_device_work: 1: line 2761: pdev=ffff90f4e369b000
[  526.454819] hv_netvsc 818fe754-b912-4445-af51-1f584812e3c9 eth0: VF unregistering: enP18059s1
[  526.457828] mlx5_core 468b:00:02.0 enP18059s1 (unregistering): Disabling LRO, not supported in legacy RQ
[  527.680118] mlx5_core 468b:00:02.0: devm_attr_group_remove: removing group 00000000074d6d6b
[  527.692794] hv_eject_device_work: 2: line 2769: pdev=ffff90f4e369b000: sleeping 10s
[  537.762575] hv_eject_device_work: 3: line 2770: pdev=ffff90f4e369b000: sleeping 10s: done: removing hpdev
[  537.768831] hv_eject_device_work: 4: line 2774: pdev=ffff90f4e369b000: hpdev is removed!!!
[  537.774313] hv_eject_device_work: 5: line 2786: pdev=ffff90f4e369b000: sent PCI_EJECTION_COMPLETE
[  537.777737] hv_netvsc 818fe754-b912-4445-af51-1f584812e3c9 eth0: VF slot 1 removed
[  537.794038] pci_bus 468b:00: busn_res: [bus 00] is released

diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
index 48feab095a14..2c0b86b20408 100644
--- a/drivers/pci/controller/pci-hyperv.c
+++ b/drivers/pci/controller/pci-hyperv.c
@@ -489,7 +489,10 @@ struct hv_pcibus_device {
 	struct fwnode_handle *fwnode;
 	/* Protocol version negotiated with the host */
 	enum pci_protocol_version_t protocol_version;
+
+	struct mutex state_lock;
 	enum hv_pcibus_state state;
+
 	struct hv_device *hdev;
 	resource_size_t low_mmio_space;
 	resource_size_t high_mmio_space;
@@ -2512,6 +2515,8 @@ static void pci_devices_present_work(struct work_struct *work)
 	if (!dr)
 		return;
 
+	mutex_lock(&hbus->state_lock);
+
 	/* First, mark all existing children as reported missing. */
 	spin_lock_irqsave(&hbus->device_list_lock, flags);
 	list_for_each_entry(hpdev, &hbus->children, list_entry) {
@@ -2593,6 +2598,8 @@ static void pci_devices_present_work(struct work_struct *work)
 		break;
 	}
 
+	mutex_unlock(&hbus->state_lock);
+
 	kfree(dr);
 }
 
@@ -2741,6 +2748,8 @@ static void hv_eject_device_work(struct work_struct *work)
 	hpdev = container_of(work, struct hv_pci_dev, wrk);
 	hbus = hpdev->hbus;
 
+	mutex_lock(&hbus->state_lock);
+
 	/*
 	 * Ejection can come before or after the PCI bus has been set up, so
 	 * attempt to find it and tear down the bus state, if it exists.  This
@@ -2777,6 +2786,8 @@ static void hv_eject_device_work(struct work_struct *work)
 	put_pcichild(hpdev);
 	put_pcichild(hpdev);
 	/* hpdev has been freed. Do not use it any more. */
+
+	mutex_unlock(&hbus->state_lock);
 }
 
 /**
@@ -3562,6 +3573,7 @@ static int hv_pci_probe(struct hv_device *hdev,
 		return -ENOMEM;
 
 	hbus->bridge = bridge;
+	mutex_init(&hbus->state_lock);
 	hbus->state = hv_pcibus_init;
 	hbus->wslot_res_allocated = -1;
 
@@ -3670,9 +3682,11 @@ static int hv_pci_probe(struct hv_device *hdev,
 	if (ret)
 		goto free_irq_domain;
 
+	mutex_lock(&hbus->state_lock);
+
 	ret = hv_pci_enter_d0(hdev);
 	if (ret)
-		goto free_irq_domain;
+		goto release_state_lock;
 
 	ret = hv_pci_allocate_bridge_windows(hbus);
 	if (ret)
@@ -3690,12 +3704,15 @@ static int hv_pci_probe(struct hv_device *hdev,
 	if (ret)
 		goto free_windows;
 
+	mutex_unlock(&hbus->state_lock);
 	return 0;
 
 free_windows:
 	hv_pci_free_bridge_windows(hbus);
 exit_d0:
 	(void) hv_pci_bus_exit(hdev, true);
+release_state_lock:
+	mutex_unlock(&hbus->state_lock);
 free_irq_domain:
 	irq_domain_remove(hbus->irq_domain);
 free_fwnode:
@@ -3945,20 +3962,26 @@ static int hv_pci_resume(struct hv_device *hdev)
 	if (ret)
 		goto out;
 
+	mutex_lock(&hbus->state_lock);
+
 	ret = hv_pci_enter_d0(hdev);
 	if (ret)
 		goto out;
 
 	ret = hv_send_resources_allocated(hdev);
 	if (ret)
-		goto out;
+		goto release_state_lock;
 
 	prepopulate_bars(hbus);
 
 	hv_pci_restore_msi_state(hbus);
 
 	hbus->state = hv_pcibus_installed;
+	mutex_unlock(&hbus->state_lock);
 	return 0;
+
+release_state_lock:
+	mutex_unlock(&hbus->state_lock);
 out:
 	vmbus_close(hdev->channel);
 	return ret;
-- 
2.25.1